Course Manual
NATIONAL TRAINING ON
CAGE CULTURE OF SEABASS
14 - 23 December 2009
Central Marine Fisheries Research Institute
(Indian Council of Agricultural Research)
Post Box 1603, Ernakulam North P.O., Kochi - 682 018, Kerala, India
and
National Fisheries Development Board
Ministry of Agriculture, Government of India
Blocks 401-402, Maitri Vihar, HUDA Commercial Complex
Ammerpet, Hyderabd - 500 038, Andhra Pradesh, India
Organizing Committee
Course Coordinator
Dr. Imelda Joseph
Course Manual
National Training on
Cage Culture of Seabass
Senior Scientist
Mariculture Division
Committee Members
Dr. Shoji Joseph
Published by
Dr. G. Syda Rao
Director
Central Marine Fisheries Research Institute
Kochi – 682 018, India
Edited by
Dr. Imelda Joseph
Edwin Joseph, V.
Susmitha, V.
Senior Scientist
Mariculture Division
Dr. Boby Ignatius
Senior Scientist
Mariculture Division
Shri K.M. Venugopalan
Senior Technical Assistant
Marine hatchery
Shri C.N. Chandrasekharan
P.A., FEMD/MD
December 2009
Shri T.V. Shaji
Skilled Support Staff
Mariculture Division
Printed at
Nissema Printers
Shri M.D. Suresh
Skilled Support Staff
Mariculture Division
Smt Susmitha V.
SRF, Mariculture Division
Citation Example:
Kandan, S. 2009. Commercialization of Asian Seabass Lates calcarifer as a candidate species for cage culture
in India. In: Course manual: National Training on Cage Culture (Ed. Imelda Joseph et al.), Central Marine Fisheries
Research Institute, December 14-23, 2009, Cochin, pp. 13-16.
FOREWORD
The culture of aquatic organisms in confined enclosures or “cage aquaculture” has grown tremendously
during the past 25 years all over the world. Cage culture is presently undergoing great innovations in
response to globalization and the growing demand for aquatic products. It has been predicted that the
fish consumption in developing and developed nations will increase by 57 percent and 4 percent,
respectively over the coming 10 years. Population growth, increased level of affluence and fast urbanization
in developing countries are leading to major changes in supply and demand for animal protein, from both
livestock and fish.
In India it has become imperative to identify new and suitable sites for aquaculture and ocean is the limit.
Cage culture is accessing and expanding into new untapped open-water culture areas such as lakes,
reservoirs, rivers and coastal brackish and marine inshore and offshore waters. Moreover, there is a growing
awareness that the possibilities offered by cage aquaculture have only begun to be explored in India.
Cage culture offers not only production of food fish, but also it forms an alternative to conventional land
based hatcheries, nurseries and even for rearing broodstock fishes in a more natural environment. It can
also be employed for rearing of oceanic fishes like tuna and the most sought after crustaceans like
lobsters.
Within the Fisheries Division of the Indian Council of Agricultural Research (ICAR), the Central Marine
Fisheries Research Institute (CMFRI), Kochi, is responsible for all programmes related to development of
mariculture. CMFRI has initiated many successful mariculture activities including breeding and culture of
edible oysters, pearl oysters, mussels, marine ornamental fishes, sea cucumbers, etc. At present as
another feather in its cap, CMFRI has pioneered in introducing successful open sea cage culture of Asian
seabass and lobsters at different locations in India. Keeping this in focus, the Institute has organized this
National Training for the benefit of the farmers, researchers and extension officers representing all the
maritime states in India, with a view to disseminate and share the information and experience in this
emerging field of mariculture, in order to enhance their competency and confidence in the area.
I am grateful to National Fisheries Development Board (NFDB), Hyderabad, for sponsoring the programme.
I express my gratitude to Dr. (Mrs.) Imelda Joseph, Course Coordinator and other committee members for
organizing the programme in a befitting manner. I thank all the faculty members from CMFRI and other
organizations like CIBA, CIFT and MPEDA. I take this opportunity to place on record my sincere appreciation
for the whole-hearted cooperation extended by the administrative, technical and auxilliary staff of the
Institute who have also contributed towards the organization of the training. I am confident that the
participants would greatly benefit from this training.
14th December 2009
Dr. G. Syda Rao
Director
PREFACE
Aquaculture aims at producing aquatic organisms of nutritional, ornamental, therapeutic and industrial
value. Cage culture is one avenue where immense scope is there for all these. Cage culture is impressive
to adopt in the fact that it provides ownership in public water with less cost of construction and reduced
capital investment, safety from predators and competitors and ultimately high yield of fish with good
economic returns.
The manual being released on this occasion contains the lecture notes presented by the faculty. On this
occasion I have great pleasure to record my whole-hearted appreciation to all my committee members
for their sincere and dedicated work. Dr. G. Syda Rao, Director, CMFRI, has extended all the possible
cooperation and guidance in organizing the Training Programme for which I am grateful to him. I am
grateful to Dr. Shoji Joseph and Dr. Boby Ignatius, Senior Scientists, Mariculture Division, for their continued
support in looking after the various academic and other field programmes. My thanks are due to Dr. A. P.
Lipton, Principal Scientist, Vizhinjam RC of CMFRI, for making the arrangements for the field visit to
cages in Kanyakumari district. I am grateful to Shri K. M. Venugopalan, Technical Staff, Marine Hatchery,
for assisting in the field work as well as in the conduct of the training programme. I have great pleasure
to extend my thanks to Mrs. Susmitha, V., Tijo Varghese and Anu Mathew, Senior Research Fellows, for
their sincere and devoted assistance in the various facets of organizing the training. The field support by
Shri M. D. Suresh and Shri T. V. Shaji, Skilled Supporting Staff, cannot be ignored on this occasion.
My thanks are also due to all the faculty members and invited speakers. I also express my sense of
gratitude to the HRD Cell, CMFRI, for their support in the conduct of the training. I place on record my
sincere thanks to National Fisheries Development Board (NFDB), Hyderabad, for sponsoring the training
programme.
I am grateful to Mr. Edwin Joseph, Librarian, CMFRI, for his dedicated contribution for the lay out and
printing of this manual in time.
I thank Dr. G. Gopakumar, Head, Mariculture Division, for being a motivation in conduct of this training,
Dr. Grace Mathew, Head in Charge FEM Division, for her support, other Heads of Divisions at CMFRI,
Scientist colleagues and friends. My sincere thanks are also due to the administrative and auxilliary staff
and research scholars, who have extended their help.
I am sure that the manual released on this occasion would enable the participants to enhance their
knowledge and competence in the field of Cage culture.
14th December 2009
Imelda Joseph
Senior Scientist &
Course Coordinator
RESOURCE PERSONS
Sl. No.
1
Name and Designation
Office Address
Dr. Syda Rao, G.
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P. O.
Kochi – 682 018, Kerala
Director, CMFRI
2
Dr. Gopakumar, G.
Head, MCD
3
Dr. Thirunavukkarasu, A. R.
Head, Fish Culture Division
4
Dr. Sathiadhas, R.
Head, SEETTD
5
Dr. Grace Mathew
Head in-charge, Mariculture Division
6
Dr. Saly N. Thomas
Senior Scientist, Fishing Technology Division
7
Dr. Imelda Joseph
Senior Scientist
8
Dr. Prema, D.
Senior Scientist
9
Dr. Sobhana, K.S.
Senior Scientist
10
Dr. Narayankumar, R.
Senior Scientist
11
Dr. Ramachandran, C.
Senior Scientist
12
Dr. Shoji Joseph
Senior Scientist
13
Dr. Boby Ignatius
Senior Scientist
Mandapam Regional Centre of CMFRI
Mandapam – 623 520, Tamil Nadu
Central Institute of Brackishwater Aquaculture
No. 75, Santhome High Road, Raja Annamalaipuram
Chennai – 600028, Tamil Nadu
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P. O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P. O.
Kochi – 682 018, Kerala
Central Institute of Fisheries Technology
CIFT Junction, Willington Island
Matsyapuri P.O. Kochi - 682 029, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
14
Dr. Jayasankar, J.
Senior Scientist
15
Dr. Ambasankar, K.
Senior Scientist
16
Dr. Kandan, S.
Assistant Director
17
Dr. Biswajith Dash
Technical Officer
18
Mrs. Shylaja, G.
Technical Officer
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
Central Institute of Brackishwater Aquaculture
No. 75, Santhome High Road Raja Annamalaipuram
Chennai – 600028, Tamil Nadu
MPEDA, Regional Centre (Aquaculture)
32, Nirmala nagar, Thanjavur – 613 007, Tamil Nadu
Visakhapatanam Regional Centre of CMFRI
Ocean View Layout, Andhra University P.O.
Behind Aqua Sports Complex
Visakhapatnam-530 003, Andhra Pradesh
Central Marine Fisheries Research Institute
Post Box 1603, Ernakulam North P.O.
Kochi – 682 018, Kerala
CONTENTS
Sl. No.
1
Title
Faculty
Page No.
Overview on mariculture and the opportunities
and challenges of cage culture in India
Dr. Syda Rao, G.
1
History of cage culture, cage culture operations,
advantages and disadvantages of cages and
current global status of cage farming
Dr. Gopakumar, G.
8
Commercialization of Asian seabass,
Lates calcarifer, as a candidate species for
cage culture in India
Dr. Kandan, S.
13
Engineering aspects to be taken care in cage
culture of seabass (Cage designs and materials,
Mooring materials, Net load calculations etc.)
Mrs. Shylaja, G.
17
Netting specifications and maintenance of
cages for finfish culture
Dr. Saly N. Thomas
23
6
Principles and practices of cage mooring
Dr. Boby Ignatius
33
7
Taxonomy, identification and biology of Seabass
(Lates calcarifer)
Dr. Grace Mathew
38
Nursery rearing of seabass fry and importance
of grading and seed transportation
Dr. Shoji Joseph
44
9
Important management measures in cage culture
Dr. Imelda Joseph
50
10
Integration of seaweed (Kappaphycus alvarezii)
and pearl oyster (Pinctada fucata) along with
Asian seabass (Lates calcarifer) in open sea
floating cage off Andhra Pradesh coast
Dr. Biswajith Dash
57
Nutritional requirements of Asian seabass,
Lates calcarifer
Dr. Ambasankar, K.
60
Feeds and feeding of seabass in hatchery, nursery
and grow out system using formulated feeds
Dr. Ambasankar, K.
66
Success in hatchery development of seabass and
its potential for commercial cage culture in India
Dr. Thirunavukkarasu, A. R. 71
Importance of water quality in marine life
cage culture
Dr. Prema, D.
81
Diseases of seabass in cage culture and
control measures
Dr. Sobhana, K. S.
87
Open sea cage culture in India A sociological perspective
Dr. Ramachandran, C.
94
17
Grow out culture of seabass in cages
Dr. Boby Ignatius
99
18
Open sea cage culture: carrying capacity and
stocking in the grow out system
Dr. Shoji Joseph
102
Growth in fleet size and investment in marine
fisheries and scope for open sea mariculture
Dr. Sathiadhas, R.
106
2
3
4
5
8
11
12
13
14
15
16
19
20
21
Geographic information systems and site selection
issues of open sea cage culture
J. Jayasankar
111
Economic analysis of cage culture of sea bass
120
Narayanakumar, R.
From 14 - 23 December 2009
Overview on mariculture and the
opportunities and challenges of
cage culture in India
Syda Rao, G.
Director, Central Marine Fisheries Research Institute, Post box No. 1603, Ernakulam North P.O.
Kochi- 682 018, Kerala, India, gsydarao@gmail.com
I
ndia is the fourth largest producer of fish in the world
expansion of these sectors. With over 8000 km of
and the total fish production is around 6 Mt per year
coastline there is immense potential for the development
and its share in the GDP is around 1.4%. The world annual
of mariculture which has taken roots only in recent years.
growth rate in aquaculture production has been 7.05%
since 1971 (FAO 2008). In 2006, aquaculture comprised
41.8% of total seafood supply. Indian aquaculture has
demonstrated a six and half fold growth over the last two
decades, with freshwater aquaculture contributing over
95 percent of the total aquaculture production. Given the
status of global fisheries, with most large fish stocks being
fully exploited or over-exploited, aquaculture production
CMFRI has developed several mariculture technologies
during last 25 years and concentrated mainly on non
finfish like green mussel, edible oyster clams pearl oysters
sea cucumbers, several species of ornamental fish, as the
scarcity or need for edible marine fish culture was not
felt. The demand for cultured marine fish is of recent
development in India.
must increase in order to maintain or increase the global
CMFRI initiated a pearl culture program in 1972 and
seafood supply per capita. Fortunately, the aquaculture
successfully developed the technology for pearl production
sector seems well positioned to succeed in this respect.
in Indian pearl oysters. Success in controlled breeding and
By obtaining control over the production process and
spat production of the Japanese pearl oyster (Pinctada
closing the production cycle for an increasing number of
fucata ) in 1981 and the blacklip pearl oyster ( P.
species, research and innovation similar to what has taken
margaritifera ) in 1984 was another important
place in agriculture is rapidly improving the
breakthrough. CMFRI also took the lead in the development
competitiveness of aquaculture, and the blue revolution
of the technology required for edible oyster farming during
is following the green revolution.
the 1970s. Intensive research on various aspects of the
India utilises only about 40 percent of the available 2.36
million hectares of ponds and tanks for freshwater
aquaculture and 13 percent of a total potential
culture of the Indian backwater oyster (Crassostrea
madrasensis) has been made and the technology has also
been developed for the hatchery production of seed.
brackishwater resource of 1.2 million hectares; in other
In India, two species of marine mussels namely the green
words, there is room for both horizontal and vertical
mussel (Perna viridis) and the Indian brown mussel (P.
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
indica) are found in rocky coastal areas. Investigation of
through large retail chains, where there are risks related
the culture possibilities for mussels was initiated in early
to retailers’ bargaining power and extensive requirements
1970s by CMFRI which resulted in the development of a
to suppliers in terms of deliveries (volume, timing, ),
range of practices for the culture of these species. Among
documentation, certification, Despite high economic
maritime States, Kerala was the first to recognise the
risks, the global aquaculture industry continues to attract
advantages of utilizing mussel farming technology in rural
new production capacity, new entrepreneurs, and new
development, from a meagre production in 1997 cultured
investors. This is a clear sign of the profitability of the
mussel production rose to 1250 tonnes in 2002 with over
industry, as high returns are the market’s signal to attract
250 mussel farms being established in the estuaries of
more investors and to increase production. There are two
Kerala.
main explanations for this development. The first is a
Considering the substantial contribution aquaculture
makes towards socio-economic development in terms of
income and employment through the use of unutilised
and underutilised resources in several regions of the
country, environmentally friendly aquaculture has been
accepted as a vehicle for rural development, food and
nutritional security for the rural masses. It also has
immense potential as a foreign exchange earner.
strong underlying growth in the global demand for
seafood. This primarily benefits aquaculture as fisheries
production cannot grow much above current levels. As
an increasing number of the world’s people, particularly
in Asia, climb from poverty to the middle class, further
growth driven by the demand for variety in protein intake
and health concerns is expected. The second is rapid
development in the technologies on which aquaculture
depend, leading to an almost continuous increase in
Aquaculture- a challenging task
productivity and quality over time. There is still much room
Aquaculture ranks among the most risky businesses to
for improvement, e.g. , in genetic material, feed
enter as an entrepreneur, farmer, or investor. The risk
formulations, disease-control, logistics, distribution, and
begins with the production process, as farms face several
marketing. With large differences in technological
substantial biophysical uncertainties related to disease,
sophistication between different species and regions, one
water environment, environmental, and climatic
can expect productivity development in aquaculture to
conditions. For many species a long production cycle from
continue to improve the competitiveness of aquaculture
fingerlings to harvest contributes to the production risk.
species, and with increased demand the production will
Market prices for most aquaculture species exhibit
be profitable. However, as new technologies are adopted,
significant volatility; market access is often restricted by
the cyclical and risky nature of the industry will also
changing trade regulations; and new competitors
continue.
continuously enter the market. There are many causes of
market risk. Obvious sources are shifts in total supply from
Cage culture
farmers and consumer demand that is not fully anticipated
The cage culture which initiated in Norway during 70s
when production decisions are made. When aquaculture
got developed into a high tech industry in many countries
products are marketed in the international arena, which
all over the world for high value fishes. The major
is the case for most aquaculture species, producers face
advantage in countries where cage culture has been
risks related to exchange rate, antidumping, sanitary and
commercialised is that they have large, calm and
veterinary regulatory changes, and other trade barriers.
protected bays to accommodate the cages safely against
Finally, aquaculture products are increasingly marketed
any unfavourable weather conditions. But in India, such
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
areas are very few and the sea conditions are
system made of butt-welded HDPE pipes, designed for
unpredictable during monsoon seasons leaving the safety
the culture of fishes such as milkfish, mullet, cobia or
of structures uncertain. Also, the Government of India or
pompano seabass, koth, ghol lobsters are used in many
any maritime States have no policies regarding commercial
countries.
mariculture and leave alone open sea cage farming. Many
countries try to venture into Indian arena to sell
aquaculture equipments including cage related products
which are suitable for their environment and may not be
to Indian conditions. But, all are reluctant to transfer
technologies suitable to Indian conditions and foreign
consultants charge exorbitantly for consultancy. Fish
farming in cages is a lucrative business for otherwise poor
coastal communities and it is an industry that is growing
rapidly in many Asian countries. In some countries and
locations, cage farming provides an important source of
fish production and income for farmers, other industry
stakeholders and investors. Of the estimated one million
tonnes of marine fish cultured in Asia, probably 80-90 %
is from cage farming. Most of the research relates to cage
aquaculture in temperate waters, an industry that has
been well established for more than 30 years, particularly
for salmon. In modern times, cage culture is also seen as
an alternate livelihood, for example, for persons displaced
by the construction of reservoirs or acquisition of land
for other developmental activities. In such a situation,
cage aquaculture has emerged as a promising venture and
offers the farmer a chance for optimal utilization of the
existing water resources which in most cases have only
limited use for other purposes.
By integrating the cage culture system into the marine
aquatic ecosystem, the carrying capacity per unit area is
optimized because the free flow of current brings in
instantaneous exchange of water and removes metabolic
waste and excess feed. Thus economically speaking, cage
culture is a low impact farming practice with high
economic returns and with least carbon emission activity.
In view of the high production attainable in cage culture
system and the presence of large sheltered coastal waters
in many countries, marine cage farming can play a
significant role in increasing fish production.
Success of open sea cage farming in India
For the first time in India a marine cage was successfully
launched at Visakhapatnam, in the east coast of India by
CMFRI in 2007. The indigenously designed and fabricated
HDPE cage was provided with a cat walk for free working
on board and stabilization. The cage net was 15 m diameter
and 6 m deep. An outer HDPE predator net protected the
cage net from damage by large predators. On top of the
cage railing, a bird net was provided to prevent bird
attacks. The entire structure was kept in position by
ballast and ropes tied to the mooring chains. The cage
was provided with a shock absorber on the mooring chain
to withstand and absorb the pressure of winds, currents
Cage is an aquaculture production system made of a
and was moored at a depth of 11 m about 300 m from the
floating frame, net materials and mooring system (with
shore line. The total net volume was 850 cubic meters.
synthetic mooring rope, buoy, and anchor) as a round or
This area being under the influence of high water currents,
square shape floating net pen to hold and culture large
strong waves, and winds and generally rough, the cage
number of fishes and can be installed in reservoir, river,
was intact. Limited number of Asian seabass, Lates
lake or sea. The design of the cage and its accessories
calcarifer, was stocked during the first trial and successful
can be tailor-made in accordance to the individual farmer’s
harvesting was carried out after four months during the
requirements. HDPE float frames installed in open
trawl ban period in the east coast. The economic analyses
unprotected water can withstand wave conditions. Round
of the operation have revealed the viability of cage culture
cage (volume depends on diameter) with floatation
in Indian waters. Other successful models are lobster
3
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
(Panulirus homarus) at Trivandrum, Kerala and seabass at
if adequate post harvest measures are adopted for live
Balasore, Orissa. At Balasore, culture of seabass in cage
fish export to countries where such fish fetch good market
was undertaken during 2009 and despite of several odds,
price. At present only shellfish is leading Indian export
a catch of 3.1 t was harvested with the active cooperation
and the scenario can be changed if we can assure post
of fishermen.
production quality for harvested marine fishes.
Opportunities for cage culture in India
An educated workforce and people with excellent animal
General
husbandry skills: sufficient number of fisheries graduates
and specialists in different areas of fish farming (Nutrition,
The Indian sub continent presents open sea aquaculture
pathology, environment ) are available in India to make
producers with a number of opportunities:
the cage farming sector technically fool proof.
A huge area to convert to mariculture farm: The Indian
Local availability of trash fish: There are 3827 fishing
coastline is extending up to 8129 kilometres and has a
villages and 1914 traditional fish landing centers in India
continental shelf area of 5.3 lakh km2. With numerous
and if proper effort is put in preserving the trash fish, they
creeks and saline water areas the opportunities for cage
can be utilised for feed, feed ingredient for compounded
culture are tremendous in India.
feed. Availability of local feed manufacturers and suppliers
Well experienced fishermen work force: India has a huge
also are added advantage.
human resource of about 14.66 million fishermen
Strong research and extension capabilities: In India there
population including adult fishermen (8.7 million), full time
are 8 National Fisheries Research Institutes, equipped
(0.93 million), part time (1.07 million),and those who are
with well experienced researchers and infrastructure
involved in ancillary activities like net making, processing
facilities. CMFRI and CIBA are doing extensive research
and fish vending (3.96 million). Development of
in marine and brackishwater aquaculture and since CMFRI
mariculture through cage farming can be taken up with a
has pioneered in open sea cage farming, it will be an added
focus on sustainability through empowering the fishermen
strength for entrepreneurs to have consultants within the
by achieving employment generation, social security and
country rather than spending on foreign experts. There
increased food security and augmenting sea food exports.
are extension researchers as well as officers in different
Many of these wild fish harvesters represent a highly
national and state level organisations and it is also helpful
trained workforce that have extensive knowledge of the
when new and novel technologies are introduced to
ocean, boat handling, net mending and maintenance, fish
aquaculture sector.
harvesting and quality control that aquaculture companies
can easily adapt to their own operations. In these cases,
previous wild fish harvesters would require only some
basic training associated with standard farm operations
and fish health management.
Strong domestic and export markets : It is a major
Marine cage culture also presents an excellent
opportunity to maintain coastal communities that are
presently reliant upon over-harvested commercial
fisheries (In the simplest terms one 6 m diameter cage is
equivalent to one ha pond on land with regard to
production and with less work).
advantage of Indian sub-continent that it has an excellent
domestic market for fish and if supply is assured during
Challenges or constraints
fishing ban seasons, the returns to the farmer will be very
Lack of clear regulations for use of open sea waters: The
attractive. Similarly export also can be enhanced for fish
Indian seas are open to all Indians and the lack of any
4
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
policy in utilisation of open waters has to be tackled in a
z
Site should be at least 6- 8m (depending on the net
positive manner. By allocating areas for cage farming, by
depth) deep over a sizable area, with sandy or rocky
means amicable to fishermen and other users of the sea
bottom
(navigation, tourism ) this can be overcome.
z
Competition arises from other uses of coastal and offshore
waters such as recreational boating, commercial fishing
and shipping
Rising costs of inputs such as energy and feed: Demand
located away from sources of pollution
z
Wind and wave action should be at moderate levels
z
Site should not be a regular fishing ground or a
navigation channel so that interference would be
and supply are not matching in many cases and therefore
hindrance for the operation
cost escalation in aquaculture operations also inevitable.
Concerns by fishermen about competition from
aquaculture: due to lack of awareness and insecure
z
Site should have an all weather access
z
Nearest beach should have required low valued fish
source to be used as feed
feeling, fishermen resist on any venture in the sea. Only
solution is to get them involved in cage culture operations
z
also. By experience in the field they will also change their
z
Before starting any new venture, it is of no concern about
environment or sustainability. But over the years, that
becomes the major concern. So before initiating cage
culture, it is better to plan out a scheme for environmental
concern over the years which will help in flourishing
aquaculture rather than killing it.
There should be adequate availability of labour and
materials
mind set.
Concerns about environmental effects of aquaculture:
Site must have good water quality and should be
Cages should be easily monitorable
Cage models
Another challenge to tackle over is in selection of cage
models and the design of the cage is directly related to
the chosen site, inshore or offshore. According to the
analysis of Loverich and Gace (1997) on the effect of
currents and waves on several classes of cages for
Technological challenges: Since the industry is new to
offshore, the most suitable cage is a self-supporting cage.
India, many stake holders will come with many offers,
However, for inshore or sheltered sites the conditions
but no proven technology is available so far.
change and gravity cages can be used. Some countries
Other challenges
Site selection
tend to move the cages offshore due to legal and possible
pollution problems, but the open sea cages face other
problem like rough sea. In all the cases, whether inshore,
Site selection is the biggest challenge in determining
offshore, or sheltered, the cage structures must withstand
commercial viability of cage culture. Identifying a location
the forces of the currents, waves and winds, while holding
that has the optimum water quality (temperature, oxygen,
the stock securely. There are a number of types of cages.
light and nutrient levels), current movements and other
Beveridge (1996) proposed four basic types: a) fixed; b)
infrastructure facilities is the most critical factor in cage
floating; c) submersible; d) submerged.
culture.
Various cage types and systems are being used for finfish
Criteria to be considered before selecting a site for cage
farms all over the world, the choice of which is usually
culture are:
determined by the following main factors:
5
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Site: The most important aspect to be considered is the
establishment of broodstock and hatchery facilities and
site in which the cages will be set up and their suitability
also to the complicated larviculture procedures involving
with regard to (i) exposure to potential sea storms, (ii)
culture of proper live feeds, their nutritional enrichment,
seabed characteristics and depth, (iii) prevailing sea
feeding protocols, grading, water quality maintenance,
conditions, and (iv) visual impact. An exposed site and an
nursery rearing and disease management. The production
increased risk of heavy storms will require cages, nets
of seed of the concerned species by development of
and mooring systems designed to resist the maximum
commercially viable technologies is essential for
registered storm strength. If the site is somewhat
development of sustainable mariculture practices, but
sheltered, a simplified mooring system and lighter rearing
many of these technologies are still in the emerging state
structure will reduce the cost of the initial investment.
and may take several years for standardisation on a cost
Should negative interactions be encountered with coastal
effective level. High value species like Asian sea bass for
tourism; submerged or low visual impact models are often
which hatchery seed as well as natural fingerlings available
considered and/or possibly recommended by the
at different locations in India is ideal to be stocked in
authorities responsible for the issuance of the farming
cages. More hatcheries are to be set up for seabass along
license.
the Indian coast for continuous supply of seed.
Cost of cages: The initial cost of the investment usually
Capture based aquaculture (CBA) is an alternative for those
represents a limiting factor particularly for those investors
species for which hatchery technology is not developed.
with a fixed budget. However, the cheapest option may
As hatchery technologies remain to be perfected for many
not take into consideration the suitability of the structures
species, fish farmers have to depend on ‘seed’ available
for the site.
from the wild. CBA has developed due to the market
Production plans: The size of the farm and cage model
may vary depending on the target pursued by the
investors. For instance, farmers aiming to produce a niche
product, or attempting to diversify production with fish
of various sizes, may prefer a large number of small cages
rather than a few large ones so that only a reduced
percentage of volume can be engaged in a selected
production.
demand for some high value species whose life cycles
cannot currently be closed on a commercial scale. CBA is
a world-wide aquaculture practice and has specific and
peculiar characteristics for culture, depending on areas and
species. The species/ groups that can be harvested as wild
juveniles include shrimps, milkfish, seabass, mullets,
pomfrets, groupers, red snappers, koth, lobsters
It is
generally considered that further development of marine
aquaculture is possible only by the increase in mass
Species selection and seed availability
production of juveniles in hatcheries. But it remains a fact
It is well known that availability of seed in adequate
that much of world’s coastal aquaculture can still be
quantities is one of the major challenges in the
expected to come only from the supply and availability of
development and expansion of mariculture. Though seed
capture-based juveniles. The species include seer fish,
production technologies have been developed for many
pomfrets, mackerel, koth, shrimps Also, there exists a good
marine finfish and shellfish species, many of these
fishery for live juveniles of different species of lobsters
technologies have not been scaled up to commercially
but very little are used for fattening. It is estimated
viable levels. The hatchery seed production of many high
conservatively that about one million of seer fish juveniles
value marine finfishes and shellfishes is complex and
of 7-10 cm and two millions of mackerel juveniles of 5-8
expensive due to the high costs involved in the
cm land by shore seines in the month of April alone along
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
the stretch of Visakhapatanam- Kalingapatnam. If only a
cages. As on today there is no indigenous scientifically
small fraction of these seed/juveniles are induced to be
developed marine finfish feed. The development of feed
brought in live condition, they form very good source of
is also very complicated and need to look into nutritional
CBA without affecting the ecosystem and livelihood of
balance for carnivorous fish, feed conversion and cost
fishermen. It will be more lucrative for the fishermen at
effectiveness. The imported feeds for seabass are sold at
the same time contributing to several fold increase in the
Rs 80/kg which is not economical for most of the farming
mariculture production. Juvenile yellow fin tuna are
operations.
available in plenty in and around Lakshadweep waters
which can be used for farming in cages.
Feed
Conclusion
With all the challenges to be faced, it is felt that with
innovations in cage culture as suitable to Indian conditions
Availability of cost effective and nutritionally balanced
can result in opening up a new horizon in Indian fisheries,
feed is another constraint for high value fish culture in
especially in mariculture.
7
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
History of cage culture, cage culture
operations, advantages and disadvantages
of cages and current global status of
cage farming
Gopakumar, G.
Mandapam Regional Centre of Central Marine Fisheries Research Institute
Mandapam Camp, Tamil Nadu - 623 520
drggopakumar@gmail.com
Introduction
The earliest record of cage culture practices dates back
to the late 1800 in Southeast Asia, particularly in the
freshwater lakes and river systems of Kampuchea.
Marine fish farming in cages traces its beginning to the
1950s in Japan where fish farming research at the
Fisheries Laboratory of the Kinki University led to the
In Europe, cage culture of rainbow trout (Oncorhynchus
mykiss) in freshwater began in the late 1950s and in
Norway, Atlantic salmon (Salmo salar) followed in the
1960s. More than 40% of its rainbow trout comes from
freshwater cages. Salmonid culture is currently dominated
by production from Norway, Scotland and Chile. Cage
culture of fish was adopted in USA in 1964.
commercial culture of yellow tail Seriola quinqueradiata
Currently many fish species have been cultivated in
and developed into a significant industry as early as
various designs and sizes of cages in Asia, Europe and
1960. Since the 1970, Thailand has developed cage
other parts of the world. Tilapia and carp predominate in
culture techniques for two important marine finfish: the
freshwater cage culture in Asia, while salmonids are
sea bream (Pagrus major) and grouper (Epinephelus spp.).
commonly farmed in Europe and the Americas.
Large scale cage farming of groupers were established
The rapid growth of the industry in most countries may be
in Malaysia in 1980. Korea started cage culture in the
attributed to the availability of suitable offshore sites for
late 1970s and by the end of 1980, cage culture of the
cage culture, well established breeding techniques that yield
olive flounder (Paralichthys olivacens) and black rockfish
a sufficient quantity of various marine and freshwater fish
(Sebastes schlegeli) was established, and developed into
juveniles, availability of supporting industries such as feed,
a successful aquaculture industry in the 1990s. Cage
net manufactures, fish processors etc., strong research and
culture of groupers (Epinephelus spp.) in the Philippines
development initiatives from institutions, governments and
has been practiced since 1980s. Mariculture of milkfish
universities and the private sector ensuring refinement and
in the 1990s led to the further growth and development
improvement of techniques/ culture systems, thereby
of the industry.
further development of the industry.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Cage culture operations
Advantages
Cage culture operation involves:
z
artisanal type or modern sophisticated ones.
Stocking: The stocking density of fish depends on the
carrying capacity of the cages and feeding habits of the
z
z
z
community (fishermen) whose income is affected by
Feeding: Many biological, climatic, environmental and
many reasons in fishing sector. It therefore acts as an
economic factors affect feeding of fish in the cages.
time. Each species varies in maximum food intake, feeding
frequency, digestibility and conversion efficiency. These
in turn affect the net yield, survival rates, size of fish and
overall production form the cage. Trash fish is the main
feed for yellowtail, grouper, bream, snapper and other
Cages make use of existing water bodies and thus it
can be given to non-land owned people of the
optimum yield and low disease prevalence.
Growth rate is affected by feeding intensity and feeding
Cage reared fish are superior in quality in terms of
condition factor, appearance and taste
secondary productivity of the sites. The optimal stocking
density varies with species and size of fish and ensures
Observation of the stock is easy in cages, therefore
feeding and routine management is easy
cultured species. For those species which are low in the
food chain, stocking will also depend on the primary and
Construction of cage is comparatively easy, be it
alternative income for such groups.
z
Harvesting is typically less labour intensive in cages
z
Fish are protected from predators and competitors
Disadvantages
z
Pond fish can make use of naturally occurring food,
while cage grown fish only have a limited access
carnivorous fish species cultured in marine cages. The
natural food since they cannot forage on their own.
shortage of trash fish is a major problem in many countries
Cage grown fish therefore needs to be fed by the
with large scale cage farming.
farmer to a much higher extent. The food that is given
Farm management: Farm management must optimize
to the cage grown fish also has to be nutritionally
production at minimum cost. Efficient management
complete, e.g. contain proper amounts of all necessary
depends heavily on the competence and efficiency of the
vitamins and minerals.
farm operator with regard to feeding, stocking, minimizing
loss due to diseases and predators, monitoring
z
When fish grown in cages instead of ponds, most
farmers opt for a high stocking density. A high stocking
environmental parameters and maintaining efficiency in
density creates a stressful environment for the fish
technical facilities. Maintenance works are also very vital
and stress damages the immune system. The risk of
in cage culture.
disease is therefore high. The risks will be increased
Advantages and disadvantages of cages compared to
further if the farmer fails to provide the fish with
land based structures
optimal water conditions and a satisfactory diet. Cage
culture can introduce or disrupt disease and parasite
The advantages and disadvantages of cage culture is
cycles, change the aquatic flora and fauna and alter
adjudged by its comparative performance with other land
the behaviour and distribution of local fauna.
based culture systems in terms of level of technology
required for construction, ease of management,
z
If proper water exchange is not there, the uneaten
adaptability, quality of the fish reared, resource use, social
feed and metabolic waste released from cages will
implications, and economic performance.
lead to eutrophication of the site.
9
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
z
z
Predators can be attracted to the cages and for that
population growth, increasing affluence and urbanization
additional protection has to be provided such as
in developing countries are leading to major changes in
predator nets
supply and demand for animal protein from both livestock
Poaching is easy because fish are confined in a small
area
and fish.
The move within aquaculture toward the development
and use of intensive cage farming systems was driven by
z
Marine cages face problems like fouling and is more
a combination of factors, including the increasing
expensive
competition faced by the sector for available resources,
the need for economies of scale and the drive for increased
z
Storms can damage the cages.
z
When cages are installed indiscriminately, its impact
suitable sites resulted in the sector accessing and
on environment and biodiversity is adverse and it will
expanding into new untapped open water culture areas
have influence on current flow and increase local
such as lakes, reservoirs, rivers and coastal brackish and
sedimentation
marine offshore waters.
Since cages occupy open water sources, it may affect
Production
navigation in the area, or reduce landscape value of
Total reported cage aquaculture production from 62
that area and are vulnerable to pollution from any
countries and provinces/regions from where data is
source.
available amounted to 2412167 tonnes (excluding China)
z
Current global status of sea cage farming
productivity per unit area. Particularly the need for
On the basis of the reported information, the major cage
culture producers in 2005 included - Norway (652306
Although no official statistical information exists
tonnes), Chile (588 060 tonnes), Japan (272 821 tonnes),
concerning the total global production of farmed aquatic
United Kingdom (135 253 tonnes), Vietnam (126 000
species within cage culture systems or concerning the
tonnes), Greece (76 577 tonnes), Turkey (78 924 tonnes),
overall growth of the sector, there is some information
and the Philippines (66 249 tonnes).
on the number of cage rearing units and production
statistics being reported to FAO by some member
Major cultured species, cage culture systems and
countries. In total, 62 countries provided data on cage
culture environments
aquaculture for the year 2005.
To date commercial cage culture has been mainly
The cage aquaculture sector has grown very rapidly during
restricted to the culture of higher value ( in marketing
the past 20 years and is presently undergoing rapid
terms) compound-feed-fed finfish species, including
changes in response to pressures from globalization and
salmon (Atlantic salmon, coho salmon and Chinook
growing demand for aquatic products. Fish consumption
salmon), most major marine and freshwater carnivorous
in developing countries will increase by 57 percent from
fish species (including Japanese amberjack, red sea bream,
62.7 million metric tons in 1997 to 98.6 million in 2020.
yellow croaker, European seabass, gilthead sea bream,
By comparison, fish consumption in developed countries
cobia, sea raised rainbow trout, Mandarin fish, snakehead)
will increase by only about 4 percent, from 28.1 million
and an ever increasing proportion of omnivorous
metric tons in 1997 to 29.2 million in 2020. Rapid
freshwater fish species (including Chinese carps, tilapia,
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Colossoma and catfish). However, cage culture systems
employed by farmers are currently as diverse as the
number of species currently being raised, varying from
traditional family –owned and operated cage farming
operations (typical of most Asian countries; to commercial
cages used in Europe and the America).
Table 1 Production of the top ten marine and brackish water
cage aquaculture countries
Country
Quantity (Tonnes)
Norway
652 306
in percent of total
27.5
Chile
588 060
24.8
China
287 301
12.1
Japan
268 921
11.3
United Kingdom
131 481
5.5
In terms of diversity, altogether an estimated 40
Canada
98 441
4.2
families of fish are cultured in cages, but only five
Greece
76 212
3.2
families (Salmonidae, Sparidae, Carangidae, Pangasiidae
Turkey
68 173
2.9
and Cichlidae) make up 90 percent of the total
Republic of Korea
31 192
1.3
production ad one family (Salmonidae is responsible
for 66 percent of the total production. At the species
Table 2 Production (tonnes) of the top ten species / taxa in
marine and brackish water cage aquaculture (excluding
PR China)
level, there are around 80 species presently cultured
in cages. Of those, one species (Salmo salar) accounts
for about half (51 percent) of all cage culture production
and another four species (Oncorhynchus mykiss, Seriola
quinqueradiata, Pangasius spp and Onchorhynchus
kisutch) account for about another one fourth (27
percent). Ninety percent of total production is from
only eight species (in addition to the ones mentioned
above: Oreochromis niloticus, Sparus aurata, Pagrus
auratus and Dicentrarchus labrax ) the remaining 10
percent are from the other 70+ species.
Species
Quantity (tonnes)
Salmo salar
Oncorhynchus mykiss
Seriola quinqueradiata
Oncorhynchus kisutch
Sparus aurata
Pagrus aurata
Dicentrarchus labrax
Dicentrarchus spp
Oncorhynchus
tshawytscha
Scorpaenidae
in percent of total
219 362
58.9
195 035
9.4
159 798
7.4
116 737
5.6
85 043
4.1
82 083
4.0
44 282
2.1
37 290
1.8
23 747
1.2
21 297
1.0
On the basis of the information gathered from the regional
Integrated cage farming
reviews, Atlantic salmon is currently the most widely
Cage culture systems need to evolve further, either by
cage-reared fish species by volume and value; reported
going further offshore into deeper waters and more
aquaculture production of this coldwater fish species
extreme operating conditions and by so doing minimizing
increased over 4000-fold from only 294 tonnes in 1970
environmental impacts through greater dilution and
to 12 35 972 tonnes in 2005 (Valued at US$4 767 000
possible visual pollution or through integration with lower-
million), with significant production of more than 10 000
trophic-level species such as seaweeds, molluscs and
tonnes currently being restricted to a handful of countries,
other benthic invertebrates.
including Norway, Chile, the United Kingdom, Canada,
and the Faroe Islands.
The rationale behind the co-culture of lower-trophic- level
species is that the waste outputs of one or more species
Most of the top marine and brackish cage aquaculture
groups (such a cage reared finfish) can be utilized as inputs
producers are found in temperate regions (Table 1), while
by one or more other species groups, including seaweeds,
the top species include salmonids, yellowtails, perch-like
filter feeding molluscs and /or benthic invertebrates such
fishes and rockfishes (Table 2).
as sea cucumbers, annelids or echinoderms. However,
11
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
while there has been some research undertaken using land
already much pressured coastal environments, there is
based systems considerably, further research is required
increasing agreement that particular emphasis has to be
on open or offshore mariculture systems.
given to the environmental sustainability of the subsector. Cage aquaculture will play an important role in
Prospects
the overall process of providing enough (and acceptable)
Cage culture has great development potential. For
fish for all, particularly because of the opportunities for
example, intermediate family-scale cage culture is highly
the integration of species and production systems in near-
successful in many parts of Asia and one of the key issues
shore areas as well as the possibilities for expansion with
for its continued growth and further development will
installation of cages far from the coast.
not be how to promote but rather how to manage it.
Even though the sea cage farming has been advancing in
However, there is also an urgent need to reduce the
many Asia-Pacific countries such as China, Indonesia,
current dependence of some forms of cage culture
Japan, Philippines, Taiwan, Vietnam and Korea in recent
systems in Asia upon the use of low value/ trash fish feed
years, it still remains to be commercialised in India. The
inputs, including those for Pangasid catfish and high value
Central Marine Fisheries Research Institute has been
species such as Mandarine fish, snakehead, crabs and
taking pioneering and massive steps towards this direction
marine finfish.
currently. The major constraint for popularization of cage
farming in India is the less availability of sheltered areas
However, the intensive cage culture of high value finfish
which are ideally suited for sea cage farming. In this
is growing fastest and there are important social and
context, the development of advanced types of mooring,
environmental consequences of this growth and
anchor and floating systems which can withstand the
transformation of the sub-sector. Similar to global tends
impact of adverse weather and currents will help us to
in livestock production, there is a risk that the fast growth
venture into more unsheltered open sea areas. Hence, it
of intensive operations can marginalize small-scale
is felt that more technological and engineering
producers and high production at different levels of
interventions in cage farming coupled with large-scale
intensity can lead to environmental degradation if not
hatchery production of high value and fast growing
properly planned and managed. Considering that most
finfishes can pave the way for the development of sea
of the cage aquaculture takes place in the fragile yet
cage farming industry in our country in near future.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Commercialization of Asian seabass,
Lates calcarifer as a candidate species for
cage culture in India
Kandan, S.
Marine Products Export Development Authority, Regional Centre (Aqua), Thanjavur
shanmugakandan@yahoo.co.in
Introduction
Asian Seabass (Lates calcarifer) a popular edible marine
Besides, advances have been taken place in addressing
health management challenges encountered while farming.
finfish commands consistent demand in domestic and
In India, seabass has been cultured in brackishwater and
international markets. It is widely distributed in Indo-
freshwater by stocking wild seed in some part of West
Pacific region and extending up to Taiwan, South East
Bengal, Tamil Nadu and Kerala. The cage culture of
Australian coast, Papua New Guinea, Arabian Sea and Bay
seabass is still in its developmental stages, even though
of Bengal and further to Persian Gulf region. In India,
the culture of seabass in different types of cages is now
seabass fishery is reported from all along the coast
established by MPEDA (in ponds), RGCA (in ponds) and
including Andaman & Nicobar Islands. Due to the
CMFRI (open waters). For the past five years, considerable
characteristic catadromous pattern of life cycle, its
development has been made in culture of the species in
population occupies a wide range of habitats starting from
cages in ponds of all bio categories and hi-tech cages in
freshwater lakes, rivers, estuaries and inshore coastal
open sea. But, many problems are remaining unsolved.
waters. However, the adult fish migrate to deeper inshore
Some problems encountered are:
sea areas for spawning and as such the early cycle is
restricted in seawater areas. Besides, exploiting its natural
resources from different environmental conditions,
seabass become a compatible species for aquaculture in
i)
from 1.0-1.5 cm. to 6- 7 cm fingerlings
ii)
iii)
Non-availability of extruded pellet feed for growout
Status of seabass culture in India
cultured in South East Asian Countries, China and Australia.
Lack of availability weaning diet required for nursery
rearing
saline water as well as freshwater conditions.
Asian Seabass in one of the prominent species being
Cannibalism during fingerling production from fry
iv)
Non availability of proper culture techniques in
different bio categories.
Several commercial hatcheries produce seeds for
Despite of all the above problems, the culture of seabass
aquaculture purpose in these countries and also evolved
in cages in the pond or in the open water is being initiated
suitable feed for growing seabass in aquaculture systems.
and standardized according to the Indian conditions.
13
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Culture technology for growing fish in cages in pond
cages can be fixed in PVC frames of floating frame, sinker
Seabass can be cultured in freshwater or brackishwater
and top lid. Around 2000 – 3000 fry can be stocked and
ponds; but cannibalism is one of the most serious
monitoring of the fries is easy in net cages. Also, the
problems in seabass culture. In order to minimize the
maintenance cost of the net cages is lesser than the
chances of cannibalism, culture is carried out in two
hapas. The only constraint is that, a floating feed should
phases, i.e. the nursery phase and grow-out phase.
be used in cages for rearing seabass. The mesh size of
the cage is 2 mm, 4 mm, 6 mm and 8 mm. The fry will
grow faster in net cages than hapas as it facilitates more
Nursery phase
The main purpose of the nursery is to culture the fry from
hatchery (1.5 – 2.5 cm) to juvenile size (6-7 cm). The
aerations and water circulation movements inside the
cages.
nursery rearing can be carried out either in earthen ponds
Food and feeding
or hapas. Nursery pond size ranges from 1000 to
During the nursery phase extruded slow sinking feed is
2000 m2 with a water depth of 80 – 100 cm. Pond with
preferred. Crumbled feed should be provided according
separate inlet and an outlet gate to facilitate water
to the requirements and subsequently the pellet size can
exchange is recommended. Pond bottom should be flat
be increased. The size of the pellet during the nursery
and sloping towards the drainage gate. Inlet and outlet
phase is highly correlated with the mouth size of the
gates are provided with a fine screen (1 mm mesh size) to
seabass fry (Table 1).
Table 1. Size of the fish and size of the feed
Size of the Fish(g)
Length(cm)
Size of feed(mm)
Type of feed
0.05 – 0.08
1.5 – 2.0
0.3 mm (Dust)
Slow sinking
0.08 – 0.40
2.1 – 3.0
0.5mm (Crumble)
Slow sinking
0.50 – 0.80
3.1 – 4.0
0.8mm (Crumble)
Slow sinking
0.90 – 1.65
4.1 – 5.0
1.0mm (Starter-1)
Slow sinking
Slow sinking
1.70 – 2.60
5.1 – 6.0
1.2mm (Starter-2)
2.70 – 4.00
6.1 – 7.0
1.5mm (Starter-3)
Slow sinking
5.00 – 7.00
7.1 – 8.0
1.5mm (Starter-3)
Slow sinking
prevent predators and competitors from entering and the
The nursery period lasts for about 32 – 45 days until it
fry from escaping the pond. Fry ranging from 1.5 – 2.5 cm
reaches the fingerlings size (5 – 7 cm). During this period,
are suitable for stocking in nursery ponds. Stocking
water exchange should be done according to the
density is between 20 – 50 individuals per cubic meter.
requirements and water quality conditions. It is to be
However, it is advantageous to conduct nursery rearing
monitored that the minimum feed wastage is occurred
of seabass in hapas because it enables closer monitoring
so as to get profitable nursery rearing of seabass.
and grading resulting in uniform size stocking and better
survival compared to open-pond rearing. It is likewise
easy to maintain and require very little capital investment.
Grading
The mechanical grader available in the market can be used
for grading the fries. Initially, once in three days and later
Nursery rearing in cages
weekly once the grading has to be done to separate the
The seabass fry can be grown to fingerlings in net cages
shooters and the bigger seabass fry. This exercise will
measuring 1 M x 1 M x 1 M, made up of HDPE. These net
give more survival rate with better growth as the seabass
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
fries are getting the suitable feed according to their mouth
Seabass cages usually are made of Nylon or Polyethylene
size. Also, the cannibalistic characteristics drastically
or HDPE Netting with varying mesh size depending on
come down due to timely grading.
the size of the fish grown.
At the stage, the fingerlings are ready for transfer to growout system and this can be harvested from the hapas by
scooping and transfer to grow-out ponds after proper
Table 2
Different cage mesh sizes and size of the fish to be
stocked
Total Length of Fish (cm)
Cage Mesh Size (mm)
7-9
counting so as to calculate the daily feeding regime.
8
9 - 11
12
11 - 15
16
15 - 18
20
grown to more than 7 - 10 cm or more than 10 – 15 g is
18 - 22
24
ideal.
22 - 26
32
26 - 32
38
32 and above
44
For open sea cage culture, the seabass fingerlings
Grow-out phase
The most common grow-out system is pond culture, in
The stocking densities in the cages vary according to the
either brackish or freshwater. A pond having minimum
size of the fish, as the culture progresses and the fish
water depth of 6 – 8 feet is required for cage culture.
grow in size the density has to be adjusted suitably. The
Fish are usually maintained in cages within the pond,
suggested stocking densities are given below:
although cage culture of fish less than 120 – 150 mm TL
Table 3 Suggested stocking density in cages based on number/
m3
and free-ranging of larger fish are sometimes combined
(Schipp, 1996).
Size (cm)
Stocking density no./Cu.M.
With aeration
Without aeration
The cages are usually 4 – 5 m2 (water surface area) and 2
7.0 – 9.0
600
350
– 4 m deep. They may hold 15 – 40 kg/m3, provided they
9.0 – 12.0
500
250
12.0 – 15.0
400
200
will stress the fish. Typically, the pond is aerated and
15.0 – 20.0
300
180
20.0 – 24.0
200
140
receives water exchange of 5 – 10 per cent of pond volume
24.0 – 28.0
150
100
per day, if necessary.
28.0 – 30.0
100
70
30.0 – 32.0
50
30
32.0 – 34.0
30
15
are cleaned off bio-fouling regularly, as poor water flow
In India, a technology has been developed and perfected
for culturing of seabass in cages in pond by RGCA, an
R&D, the arm of the Marine Products Export Development
Feed
Authority. In this method, the pond cages having the
At present, seabass culture is facing the non-availability
dimension of 2 M x 2 M x 1.3 M (approx. 5.0 Cu.M.) using
of floating extruded pellet feed which is the major
PVC pipe frames of 40 mm (floating frame), 32 mm
constraint. However, few companies in India have come
(sinker), 25 mm (top lid). The cages are fastened to the
forward to manufacture feed for seabass culture, which
bamboo or wooden poles of the catwalks fixed in the
is highly suitable for cage culture. Even though, trash
ponds. The catwalks are provided for the purpose of day-
fish are given widely for the culture at present in many
to-day management activities, such as feeding, sampling,
places for sustainable aquaculture, the pellet feed is the
grading etc.
highly recommended. The feed should be given twice
15
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
daily in the morning hours, 6 – 7 A.M. and evening 6 – 7
If fish is weighing an average 1 kg weight, around 100
P.M. at the rate of 8 – 10% total biomass in the first 2
nos. of fish can be stocked in the 5 m3 area. The harvest
months of culture. After 2 months, feeding is reduced to
of the fish grown in the cage can be done with minimum
once daily and given during late evening at the rate of 2
labors and effort. Around 10 tons production can be
– 5% of the total biomass. The floating pellet feed should
harvested within 3 – 5 hours from 100 cages. As the fish
be given only when the fish swim near the surface to eat.
are grown in the cages is giving good muscle structure,
The suggested feeding schedule for extruded pellet feed
taste and flavor, it is always fetching an average rate of
is given below:
Rs.150 – 180 in India (the price vary according to the
Table 4 Suggested feeding schedule, as % of body wt., type of
feed, etc.
Size (cm)
Feed as % of
body weight
Pellet Size
(mm)
Type of feed
7-9
10 - 12
13 - 15
15 - 18
18 - 20
20 - 22
22 - 25
25 - 27
27 - 30
8.0
7.0
6.0
5.0
4.0
3.5
3.0
2.6
2.2
2
2
3
5
5
7
7
9
9
Slow sinking
Slow sinking
Slow sinking
Floating
Floating
Floating
Floating
Floating
Floating
30 - 35
2.0
11
Floating
FCR
local demand) and in export, fetching US$ 4 – 5 per kg.
Note: For open sea cage culture, the mesh size of the cage
is same and only the width of the cage (circular or
rectangular) will vary according to the stocking density and
environmental conditions prevailing in the open sea. The
frame for open sea cage culture, HDPE material is
recommended. Stocking density, feed and feeding type and
all other aspects are almost similar to the culture of seabass
in cages in the pond.
Conclusion
In India, the aquaculture is centric to the shrimp/scampi
production and these two species are contributing in total
of 52% towards export. The freshwater fish produced
through aquaculture is mainly catering to the domestic
market only. In Indian seawater many finfish and shell
For any aquaculture practice, the FCR is the determining
fishes are abundant for aquaculture, which is economically
factor for the economic viability of the fish culture for
important, the seabass (Lates calcarifer) fish is occupying
domestic or export and also the cost of production per
the main role at present as it is a candidate species for
unit. For seabass, 1: 1.2 FCR is recommended by using
cage culture as it has completed a value chain approach
extruded pellet feed and 1: 5 – 7 is the observed FCR by
from seed production, nursery rearing, grow-out and
using trash fish or farm made feed.
marketing & export by MPEDA through its R&D Institute
Production, harvest & marketing
In a 2 M x 2 M x 1.3 M cage, around 80 – 100 nos. is the
recommended stocking density (biomass) in pond system.
– RGCA.
Note: The above text and results presented here are based
on the various demonstrations conducted on culture of
seabass in cages in ponds by MPEDA-RGCA.
16
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Engineering aspects to be taken care in
cage culture of seabass (Cage designs and
materials, Mooring materials, Net load
calculations etc.)
Shylaja, G.
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
shylusuresh@rediffmail.com
Aquaculture systems are very diverse in their design and
mechanical wear and corrosion. Repairs and salvages are
function. The three most basic categories of culture
more difficult and in some cases access may be denied to
systems are: i) Open systems, ii) Semi closed and iii)
some structures during a storm. Because of all these
Closed systems.
reasons the design of an aquaculture cage system is very
Modern cage culture began in 1950’s with the advent of
synthetic materials for cage construction. The major
advantage of cage culture is use of existing water bodies,
technical simplicity, simplified harvest and low capital
cost compared with land based farm. But it has got certain
complex in nature and of course the most difficult task.
Hence, it is essential to select a proper site, ideal
construction materials and proper designing, suitable
mooring and good management etc in bringing out a cage
culture production more profitable and economical.
disadvantages like feed must be nutritionally balanced,
Four different types of cages are fixed, floating,
pollution, out break of disease, vandalism etc.
submersible and submerged (Fig. 1)
Engineering considerations in the design of
cages
The sea is perhaps the most difficult
environment for Engineering. The sea can
generate great storm forces on any floating
or sea bed mounted structure and storm
events occur randomly. The constant 24 hour
per day bending compression and tension
within structural member are optimum
conditions for fatigue. Similarly constant
motion in a corrosive fluid is ideal for
Fig. 1 Characteristics of different types of cages
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Fixed cage consists of a net supported by posts driven
into the bottom of a lake or river, they are completely
inexpensive and simple to build, but their use is restricted
to sheltered shallow sites with suitable substrates. The
floating cages have a buoyant frame or collar that support
the bag, they are less limited than most other cages in
terms of site requirements and can be made in a great
variety of designs ,and are the most widely used ones.
The submersible cages rely on a frame or rigging to
maintain shape. The advantage over other designs is that
its position in the water column can be changed to take
advantage of prevailing environmental conditions.
Generally these cages are kept at the surface during calm
weather and submerged during adverse weather. The
submerged cages can be wooden boxes with gaps
between the slots to facilitate water flow and are
anchored to the substrate by posts or stones.
The major components of a cage farm are a) cage bag, b)
floats, c) frame, d) service system, e) mooring system and
f) anchor system.
The cage frame, nets used for cages and the mooring
system has to withstand all types of weather conditions
all year round. Net failure is an important source of fish
loss in cage culture systems. So while making a net for a
specific purpose many considerations are taken into
account such as the forces applying on the net, the kind
of materials the net and rope frame made from and the
way in which they are tied. The main forces on any net
structure are those arising from winds, waves and currents
and from the interactions of the cage structure and its
mooring systems with the resulting movement.
Pectra or Dynema have appeared. The nets are stretched
vertically with weight at the bottom of the cage or
fastened by rope to the frame work. The tensile (breaking)
strength of the nets can be tested to check its load
carrying capacity by British Columbia Method, wherein a
mesh is extended until it ruptures under the applied load.
The apparatus used can indicate the load at the point of
rupture. The testing machine is operated at rate of
elongation which is both constant and within the
prescribed limit.
One important aspect in the determination of cage bag
size is stocking density and optimum carrying capacity. The
shape of the cage is also another point under consideration.
Observations made on the swimming behavior of the fish
suggest that circular shapes are better in terms of
utilization of space. Corners of rectangular shapes are little
utilized. It is assumed that depths greater than 10-12 m
would be poorly utilized by fish and a cage depth of 3-10 m
be acceptable for most of the species. Circular cages are
having least perimeter for a given area, hence reducing the
material cost. Fig. 2 shows the perimeter lengths of
different cage shapes for the same area of 16m².
Cage bag
The three major functions of cage bag are a) keeping the
fish stock together, b) protecting the stock against
harmful external influences, and c) allowing free water
exchange between the inside and outside water.
The net is normally flexible and made of synthetic nylon
or polythene fibers reinforced with polythene ropes
although recently new stronger materials like sapphire,
Fig. 2 Perimeter lengths of different cage shapes for 16m² area
It is advisable to have the net meshes impregnated with
a special anti-fouling material to prevent biofouling. The
upper side of the cage bag above the surface is joined to
the hangers in the brackets near the hand rail for lateral
protection. Surrounding vertical and horizontal ropes
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
which are used for joining the net to the rings reinforces
the cage bag. The cage bag comprise two nets one inner
net in which fishes are placed and an outer or predator
net to protect the fishes from predators. A bird net also is
provided for protecting it from fish eating birds.
Floats
Floats provide buoyancy and hold the system at a suitable
level in the surface of the water. This also holds the shape
of the cage structure. Common floatation materials include
metal or plastic drums, HDPE pipes, rubber tiers and metal
drums coated with tar or fiberglass. Fiberglass drums are
Service systems
This is the system required for providing operating and
maintenance services, for e.g. feeding, cleaning,
monitoring or grading. One way to provide this is by a
catwalk around the cage. Some cages use their floatation
collars made of metal or plastic pipes with or without
additional internal or external floats. But polyethylene
has the strength, flexibility and lightness necessary for
the catwalk in the cage.
Mooring system
preferred as they can last for many years although the
This holds the cage in suitable position according to the
initial cost is comparatively high. Styrofoam blocks covered
direction and depth decided in the design. The mooring
with polyethylene sheets provide good buoyancy. The
joints the cage with the anchor system. A mooring system
buoyant force varies depending of size and materials used.
must be powerful enough to resist the worst possible
Frame
combination of the forces of current, wind and waves
without moving the break up. Wind and current forces
The frame can be made of galvanized steel aluminum,
are proportional to the square of the velocity. Thus an
timber and different plastic materials. The frame should
increase in current from 1 knot to 2 knot will generate 4
be mechanically strong, resistant against corrosion and
times the drag on a rigid submerged body. A change in
easily repairable or replaceable. The cage has collars of
the mooring system will change internal load on the cage
HDPE for structure and the same time for floatation and
system. Wave forces are much more difficult to compute
for ballast. The HDPE pipes are highly flexible structure
because the dynamic response of the system depends on
and are used in most of the circular cages. The cage has
so many factors. The materials used in the mooring line
two floatation pipes filled by expanded polystyrene as a
are sea steel lines, chains, reinforced plastic ropes and
precaution in case of damage avoiding loss of floatation
mechanical connectors. The mooring force capacity
force. The ballast pipe will have holes for the free flow of
depends on both the material and size and can be adjusted
water and metal lines are used inside for increasing weight.
to the requirements. Attachments to the system are by
The hand rail pipe will not have any material inside. The
mechanical connectors and ties.
pipe ends will be jointed by using a welding process for
plastics.
Two types of mooring systems commonly used are
multiple points and single point. The former is more
The two pipe rings for floatation and brackets will join the
common and involves securing the cage in one particular
hand rail. These brackets will give support to the rings
orientation while with the latter the cages are moored
and at the same time it will form a part of the catwalk.
from one point only, allowing them to move in a complete
The brackets made of galvanized steel to avoid corrosion
circle. Single point mooring tends to be used with rigid
and be fitted to the diameter of the pipes. The maximum
collars. They use less cable and chain than multiple point
height of hand rail should be approximately 100 cm and
mooring and, because they adopt a position of least
minimum width for cat walk approximately 60 cm.
resistance to the prevailing wind, wave and current forces,
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
both inter cage forces and tortional forces at linkages are
reduced. Single point mooring system also reduces the
enormous net deformation than the conventional mooring
system. They distribute wastes over a considerably larger
area than those secured by a multiple point system. Fig.
3 & 4 shows single and multiple point mooring systems.
To avoid the possibility of bag shape deformation caused
by possible high currents, the mooring uses a system of
six joint points to the cage, three in the upper side to the
floating pipe and the other three in the lower side attached
to the ballast. This connection up and down in the cage
assures to maintain the shape in position irrespective of
the currents. The orientation of cages with multiple
mooring depends on the nature of the site and the type
and group configurations of the cages. If the currents are
strong it may be best to secure cages in the position of
least resistance to the prevailing wind and current force,
Fig. 3 Single point mooring system
There are a variety of methods of using a single and
multiple point moorings.
mooring system are principally dynamic. It is important that
mooring line must have a high breaking strength and can
absorb much of the kinetic energy of rapidly changing
forces (wave and wind) otherwise these forces will be
directly transmitted to anchors. Chains are used as mooring
line, it is extremely stronger but it is heavy and used in
conjunction with synthetic fiber rope, Synthetic fiber ropes
are composed of nylon, PE, PES, PP etc. Stainless steel
chain is suitable for marine use, but it is expensive. Mild
steel chain with low carbon and manganese contents has
been widely recommended for cage anchorages.
Total length of the mooring line should be at least three
times the maximum depth of water at the site and where
the rope joins the chain a galvanized heavy duty thimble
should be spliced in to the rope and a galvanized shackle
of the appropriate size used to connect the chain to the
rope. The chain is connected from the anchor to a float
positioned 10 m or so from the cage and a section of rope
is used to link the float to the cage. The buoy minimizes
the vertical loading on the cages and must be sufficiently
large to support the mass of the chain and to resist the
vertical forces imposed by the cages on the mooring
system. Under shock loads, the chain /buoy acts as a
spring absorbing much of the energy that would otherwise
be transmitted to the anchor. The possible shock loads
can be counteracted using a system of hung weights
located between the multi connector pipe and the anchor.
This system ensures soft movements of the cage with
the current by absorbing possible shocks. The vertical
position of the weights depends on the forces acting upon
it, thus operating as a shock absorber.
Anchor system
Fig. 4 Multiple point mooring system
Mooring line must perform two functions: they must
withstand and transmit forces. The loads imposed on a cage
The simplest and cheapest type of marine anchor is the
dead weight or block anchors, which typically consist of
a bag of sand or stones or a block of concrete or scrap
metal. Concrete block anchors may simply be fabricated
with reinforcement. The anchor is connected to the
mooring system by chains and ropes. The anchor system
is normally formed by a system of concrete blocks joined
together, by chains and connected to a buoy by a braided
rope. Several concrete blocks instead of one, make the
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
setting of the system easy. These mooring and anchor
systems allow the cage to be disconnected easily and
quickly in case of bad weather and the cage can be towed
to a safe place without loosing its shape.
Mooring maintenance
Cage mooring is a dynamic system which must respond
to motion under load every minute of the period for which
it is established. Maintenance is critical to ensure that
components are physically sound and that linkages secure.
Wear and tear of the parts namely chain links, brackets,
shackles, splicing eyes, need to be checked periodically
and bolts and shackle pins need to be tightened. Proper
maintenances of the entire system gives more life to cages.
Specifications of the CMFRI cage at Munambam, Kochi
The chosen site was having an average velocity of current
1m/s, depth 10 m, and muddy sea bottom. The loads were
divided in to two types:
a) Static loads, which are vertical and are caused by the
action gravity with reaction in the buoyancy of the cage.
These depend on the area and density of the netting,
weights of the frame components, weight of rigging,
weight of the ballast and opposition in the floatation force.
b) Dynamic loads, which are mainly horizontals and are
caused by the current, winds and waves with reaction in
the moorings and anchors of the cage. These depend on
the materials used, shape of the panel, size of the mesh,
current velocity and density of water.
To compute the static loads in the cage the relation
between the weight of the cage with its components like
the descendent force and the capacity of floatation the
ascendant force was estimated. The weight was
computed for three conditions:
a)
Clean cage in air
b)
Clean cage in water
c)
Foul cage in water
In order to compute the weight of the cage in water, the
densities of the materials used must be established. For
the cage to float, the static loads acting on the structure
( i.e. weight in water) must be counterbalanced by
buoyancy forces. The buoyancy of the collar is dependent
upon the upward force acting on those components
wholly or partially immersed in water and is equal to the
weight of water displaced.
The buoyant forces can be calculated by using the formula:
FB = Vw Qw-Vm Qm
FB = buoyant force (kg)
Vw & Vm are the are the volumes of water and
floatation material (m³)
Qw & Qm are the densities of water and floatation
material (kg/ m³)
The loads caused by the currents, wind and waves against
the cage were considered to be the dynamic forces. These
forces act on different parts of the cage, but all of them
drag and deform its shape. The knowledge of these forces
is required for the computation of the mooring and
anchoring system. The current act mainly on the cage
bag and rigging under the water, the load depends on the
current velocity, density of water, material, shape and
size of mesh. Water flowing through a mesh or netting
imposes loads which are transmitted to the supporting
frame, collar and mooring system.
Wind and current forces are proportional to the square of
the velocity. Thus an increase in current from 1 knot to 2
knot will generate 4 times the drag on the rigid submerged
body. Wind forces act mainly on the cage superstructure
formed by hand rail, brackets and free board netting.
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
The general equation to calculate the current drag is
Fx = 1/2 Cd.µAv² (expressed in KN)
Where Fx = current drag
Cd = coefficient of drag
p = density of sea water in T/m³
A = area normal to flow in m²
V = incident current velocity m/s
The wave forces acts mainly in the ring area of the cage.
It is very difficult to compute the wave forces as the
dynamic response of the system depends on so many
factors. To calculate it, the horizontal and vertical orbital
velocities of the water particles must be known. These
can be derived from the information on prevailing wave
periods, wave height and water depth at the site.
Wave force (Fw) = Kd.pµ²A
Where Kd is the coefficient similar to Cd in netting whose
value depends on the material and shape of the collar
p
= density of sea water
µ
= horizontal component of wave particle orbital
velocity (for marine cage it s taken as 2m/s)
A
= area of the cage collar perpendicular to the wave
train
The moorings and anchor system and their components
were proposed based upon the calculated forces on the
cage. For a particular current velocity a fouled cage with
total load (sum of the loads acting on each component)
was calculated. Based upon the maximum load estimated
a gabion box made of PP with copper lining containing
three compartments of 1t each (total 3t) capacity was
filled with stones and used as the mooring system.
Specifications of other materials used for the cage are
given in Table 1.
Table 1 Specifications of the parts used:
Part
Material
Size /quantity
Floating pipe innerFilled with PUF
HDPE140mmø 10kg/cm²(PE100 grade material
6m dia
Floating pipe outer
HDPE140mmø 10kg/cm²(PE100 grade material
8m dia
Middle ring
HDPE90mmø 10kg/cm²(PE100 grade material
catwalk
Base supports
250mm,HDPE
8 nos.
Vertical supportsFixed with T joints ,
using fusion welding as well as with
SS bolts and nuts
90mm,HDPE
0.8 m height16 hooks
Diagonal support
90 mm, HDPE 10 kg pressure
8 nos
Buoys,filled withPUF,
350mm dia with end caps(10 kg)
Mooring clamps
14mm,4"mooring clamps
Mooring chainMS
10mm
3 nos
Ballast pipe
HDPE,63 mm ,circular
Mooring swivel
MS
Outer net, Braided HDPE,
3mm/80mm square mesh
Provided with SS rings of 12mm thickness,for
connecting to the cage frame
7m dia&5m depth, 18 rings
bottom12 ring top
Inner net, Twisted HDPE net
1.25 mm/30-35mm mesh size
With SS rings
6m dia & 5.3 m depth12 rings
top
Bird net,1.25mm/80 mm
twisted HDPE
6m dia
Hapa,Nylon with 8/10 mm mesh
2.5x2.5x3 m rectangular shape
Chain 80 grade MS 10mm
3T working load,7T stretching load,11 breaking load
D shackle 1’’,1/2’’&3/4" MS
(3T,0.5T,3Tworking load)
Swivel 1’’ forged steel 80 grade
3T working load
Solar blinkers
Water proof shock resistant red colour blinking light
8m dia
3 Nos
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Netting specifications and maintenance of
cages for finfish culture
Saly N. Thomas
Fishing Technology Division
Central Institute of Fisheries Technology, CIFT Junction, Matsyapuri P.O.
Cochin - 682 029, India, salynthomas@gmail.com
A cage is a space enclosed with some type of mesh
or 5×5 m, with a depth of 2-3 m while rectangular types are
forming a container for aquatic animals to grow. It is
6×3 m, with a depth of 3 m. In Korea, the floating cage
typically box-shaped or tube like structure with a rope
system consists of the cage and a frame to support the
system which supports the netting material, gives shape
nets. In India, rectangular cages of 10mx5mx2.5m are used
and allows for tying to the raft unit. In box type cages,
for the culture of Indian major carps.
the cage is constructed of four panels at the sides and
one bottom panel. Anti-predator nets are deployed around
Basically there are 3 types of cages:
the cage to prevent entrance of predators such as sharks
Hapa cage is for stocking of the fish during the early
and sea lions into the cages. An additional net would be
nursery phase (Fingerlings to a Total Length of about 10
provided on top of the cage to prevent bird predation.
cm). This is made of very fine-meshed nylon net. It is
used for rearing fry to fingerlings. Fry measuring 1–6 cm
Types of net cages
are initially stocked in this cage.
The cages usually are of two types: fixed and floating.
Nursery cage is used during the later nursery phase.
The floating cages are interlocking cages suspended in a
Usually PE net is used for the net bag. This cage is stocked
bamboo/wooden/ polyethylene frame. The cage is floated
with 10 cm fingerlings till they reach a size range of 15–
by either bamboo raft or styrofoam floats, and is held in
20 cm.
place by heavy anchors.
Grow-out cage is used for the grow-cut phase where
The dimensions and mesh sizes of the cages are dependent
the cultured fish reach marketable size of 30 cm and
on the species cultured and size. The mesh sizes of the cages
beyond. The netting used is usually PE net.
depend upon the type of cage. In Japan, circular and square/
rectangular floating cages are used, whereas in Norway
floating cages are not only circular, square/rectangular, but
Broodstock require cages of mesh sizes larger than 50
mm.
may also be hexagonally shaped. Cages that are either
The rope which is used for the main and hanging lines of
cylindrical or spherical are used in West Germany. In
the hapa and nursery cages is PP/PE rope (6 mm diameter),
Singapore, the farmers use the more conventional square
while for the grow-out cages, PP/PE rope of 10 mm
(cuboidal) cages. The square type usually measure 2×2, 3×3
diameter is used.
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
The frame which is used to hold the interlocked cages
forces on a net impoundment structure are based on the
together in place also serves as a catwalk and working
highest wave expected to occur in the design life of the
platform. A frame made of bamboo is preferred over a
structure. As fouling or surface debris drastically affect
wooden one mainly due to economic reasons. Besides,
the coefficient of drag, this factor must be considered.
the bamboo frame also acts as a floatation device.
Fouled nets create twice the resistance to tidal current
as the same net when clean (Milne, 1970). The nets must
As net bags are subject to damage by floating debris, large
be designed to withstand the sum of the forces, assuming
carnivorous animals and other agents, often a second
that all the forces are at some moment acting in the same
larger mesh net is used outside the net to provide
direction. If two nets are used, loads on the supporting
mechanical protection for the confinement net. The two
structures will be the sum of the loads imposed by each
nets must be placed in such a way that they do not rub
net.
each other, or one or both nets will be damaged by
abrasion. E.g: the outer netting can be of HDPE braided
twine of 3 mm diameter and mesh size 80 mm. There can
be an upper selvedge of netting made of HDPE of 4 mm
diameter braided twine of the same mesh size and 80
mm mesh size. This selvedge portion should be of 0.5
meter stretched length or equal to the length of the
brackets/rings above the upper ring structure whichever
is larger. Inner netting can be of HDPE twisted twine of
1.25 mm diameter and of mesh size 25 mm. An upper
The aquacultural net enclosures should have good tidal
flushing. Water flowing through the net will impose loads
on the net and supporting or mooring structure. Kawakami
(1964) developed the following Equation 12.9 to describe
the load imposed on net structures due to flow at right
angles to the net. The force on 2.50 cm mesh nylon net
by a 1 m/s current is 0.42 N/mesh in the unfouled
condition and 5.1 N/mesh after one month of immersion
in sea water.
selvedge of netting made of HDPE twine of 2 mm diameter
Nets enclosing fish are subject to damage by floating
and with 25 mm meshsize. This selvedge portion should
debris, large carnivorous animals and other agents. A
be of 0.5 meter stretched length or equal to the length of
relatively small hole in the enclosure net can result in
the brackets/rings above the upper ring structure
loss of nearly all the fish. Hence, it is often wise to use a
whichever is larger.
second larger mesh net outside the confinement net to
provide mechanical protection for the confinement net.
Design Considerations
The two nets must be placed in such a way that they do
Designing of net structures require several forces to be
not rub each other, or one or both nets will be damaged
considered; the main being static and dynamic loads.
by abrasion. As all nets require periodic maintenance for
Static loads include the weight of the structure (net,
cleaning or repair before design it must be decided
support, and other structural parts), and added loads due
whether the panels will be pulled out of the water for
to maintenance and operations. Dynamic loads include
this work or divers will be used. If the panels must be
forces generated by wind above the water surface, waves
removed from the water, some means to prevent fish
at the air-water interface, and currents (particularly tidal
escape will be necessary. The panels must also be small
currents) in the water. Additional dynamic loads may be
enough to be manipulated by the handling technique
encountered due to collection of floating debris, collision
chosen. Panel weight will be actual panel weight plus
with water craft or large predators or other similar
weight of fouling. The following factors are generally
conditions. Effects of corrosion and fouling add to it. Wave
considered in the design and operation of culture cages:
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
z
z
It is advisable to put floating cages underwater to avoid
netting without further process, hence it follows that
wind action and also to reduce algal growth
monofilament yarn is a netting yarn also. The Twisted
Use cage materials available within the locality to
reduce the costs
z
netting yarns (netting twines) are made by a series of
processes.
z
Fibres twisted together to form a single yarn.
z
A number of single yarns are twisted together to form
Before setting out the antifouling impregnated nets
they should be dried so that the antifouling stays on
a strand or ply.
the net.
z
Consider the cost and durability of the materials
z
Net size: It is better to design the size of net cage to
suit the breadth of the netting rather than on a
preselected size.
z
z
Three strands or ply are twisted together to form a
netting twine.
Synthetic materials are predominantly used for
construction of net cages. Synthetic fibres are produced
entirely by chemical process or synthesis from simple
Size of species: Net mesh should be smaller than the
basic substances such as phenol, benzene, acetylene etc.
fish size to avoid escape of the fish through the
As compared with vegetable fibres, they have better
meshes.
uniformity, continuity, higher breaking strength and are
more resistant to biodegradation. Depending on the type
z
z
Nets should have sufficient strength to withstand
of polymer, synthetics are classified into different groups
different forces encountered
and are known by different names in different countries.
Net bag should have suffiecient looseness. To get a
uniform spreading and flexibility to the bag 20-30%
of excess net is to be used than the actual cage size
z
Aeration can enhance water quality, reduce stress,
improve feed conversion efficiency and increase
growth and production rates. Aeration can improve
cage production by 20 percent or more.
z
Altogether 7 groups are developed; polyamide (PA),
polyethylene (PE), polypropylene (PP), polyester (PES),
polyvinyl chloride (PVC), polyvinylidene chloride (PVD) and
polyvinyl alcohol (PVAA).
The synthetic netting yarns used in Indian fisheries sector
are polyamide, polyethylene and polypropylene. PA and
PE are the most commonly used fibres for netting while
PP and PE are used for ropes. The material strength of
Leave at least 10 feet between cages and keep cages
net panels when exposed to sunlight (UV), wind, rain,
away from weed beds. Weed beds and overhanging
acid rain, etc. get reduced. This process is called
trees can reduce wind circulation and potentially cause
weathering. Even though all fibres, irrespective of natural
problems.
or synthetic are prone to degradation on exposure to
weathering, the problem is severe with synthetic fibres.
Netting materials for cage construction
The main factor responsible for weathering is the sunlight,
Netting yarn is a textile product suitable for the
i.e. the ultra violet part of the sun’s radiation. Polyvinyl
manufacture of netting and can be knitted into netting
chloride (PVC) is the material that is most resistant to
by machine or by hand without having to undergo further
weathering, followed by PE and PA; PP has the shortest
process. Yarn is made into a netting by twisting or
lifetime. The lifetime can be increased by adding a
braiding. Monofilaments are used directly for making into
coloured (black) antioxidant, so that development of
25
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
weathering is reduced. The resistance of netting materials
Polyethylene is preferred for its high breaking strength,
to abrasion, i.e., abrasion with hard substances such as
durability, high resistance to abrasion and cheaper cost
frames, sea bottom and net haulers, or abrasion between
when compared with other available materials like
yarns/twines is important in determining the life of a net.
polyamide, polyester, polypropylene etc.
Another material recently introduced is Ultra high
z
Polymide (PA) and polyethylene (PE) netting are readily
molecular weight polyethylene (UHMWPE) available as
available locally. Knotless polyamide netting of
Dyneema. It is very advantageous as aquaculture nets
210Dx2x2 is popular for making cages that are to be
due to the low diameter, favorable weight/strength ratio,
used for stocking young fish fingerlings and prawns
low elongation and nil shrinkage in water which helps
as the material has a smooth surface and there is
the mesh size to remain stable during normal use of the
minimal abrasion on the fish when the cage is lifted
netting. The resistance of Dyneema nets to UV light and
up during net change. PA is expensive and costs about
abrasion is high, guaranteeing that nets last longer.
Rs. 350-470/kg. However, it has a very high breaking
Selection of netting material
strength and abrasion resistance. Its fibre deteriorates
if subjected to prolonged direct sunlight and hence it
The following factors are to be considered for selection
is classified as having medium durability. The material
of suitable net material for the construction of cages:
being soft, can also be cut through by crabs and fish
Synthetic fibres are preferred over artificial or natural fibres
with strong dentition and the cultured fish can escape
because of their durability and strength.
z
through gaps made in the cage
Cages made of synthetic fibres are convenient to use
as they can be easily folded and are light to handle.
z
operators because it is cheaper and protects better
They are also easy to install and to remove. It is not
against damage caused by crabs and fish, although
surprising that many floating farms use such materials
large-sized crabs can still bite through the material. It
rather than rigid metal cages for rearing the fish
z
is the cheapest of the synthetic netting materials
The netting yarn should maintain its shape, e.g.
available, priced at around Rs. 200-275/kg, viz. around
monofilament netting, suitable for gill-netting, is not
half the price of PA netting
suitable as cage material as it tangles and folds up
easily
z
z
z
PE netting is available in various specifications of
Denier and ply and also in knotless and knotted forms.
The material should be durable, resistant to abrasion
The type that is selected would depend on the species
and has high breaking strength
and size of fish stocked. PE has also high breaking
The material should not be so heavy as to make
handling difficult e.g. thicker netting material even
though durable and resistant to crab bites/abrasion
would be heavy at cleaning time especially when it is
fouled.
z
Polythylene netting is generally preferred by cage
strength and abrasion resistance. However, like PA, it
is to be stored away from direct sunlight, viz. in the
shade. When used at the farm, the portion of the cage
above water lasts for 3 years, whereas the rest of the
cage which is submerged in the water lasts for 5 or
more years. PE netting is usually for making cages for
With the exception of the hapa net, cages are usually
nursery and grow-out fish while for hapa, PA is
constructed of polyethylene (PE) material.
preferred
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Table below lists the synthetic fibres that are suitable for
distance between the knots on a stretched mesh (Fig. 1).
use as fish cages.
In a hexagonal mesh, the mesh size is given as the distance
Table 1 Comparison of important characteristics of synthetic fibres
Properties
PA
PE
PP
PVC
PES
PVD
PVA
Specific gravity
1.14
0.96
0.91
1.35-1.38
1.38
1.70
1.30
Melting point °C
240-250
125-140
160-175
180-190
250-266
170-175
220-230
Durability
Medium
Medium
Poor
Very high
High
High
High
Breaking strength
Very high
High
Very high
Low
High
Low
Medium
Extensibility (wet)
High
Medium
Low
High
Low
High
High
Resistance against weathering
Medium
Medium
Low
Very high
High
High
High
Abrasion resistance
Very high
High
Medium
High
High
High
High
Cost
Very high
Low
High
High
Very high
High
High
polyamide (PA) is the most commonly used material for
between the two longest parallel bars. Mesh size may,
the fabrication of net bags, as the material is strong and
however also refer to bar length, which makes this
not too stiff to work with. PE is also used to some extent
expression rather confusing.
because it is more resistant to fouling as the surface is
smoother: however, it is stiffer to work with. Polyester
(PES) has also been tried. Nylon used for nets is made as
a multifilament twine consisting of several thin threads
spun together to make a thicker one. The advantage with
multifilament is that the thread is easy to bend, easy to
work with, tolerates more loads and is more resistant to
wear/rubbing. In contrast, monofilament is a single thread
as used in a fishing line. It can be made of PE; it is stiffer
and more vulnerable to chafing than a multifilament. Nets
are either knotted or knotless.
Mesh size
Another factor which decides how the net panel is
standing in water is how the net is stretched in the length
and depth wise directions. This is called the hanging ratio
of the net (E) which is the ratio between the length of
the stretched net panel (Lm) and the length of the rope/
line where the net is fixed (top line) (L):
E = L / Lm
Normally E for net bags for fish farming is in the range
0.6 – 0.9, while for a fishing net, E is between 0.4 and
0.6, meaning that netting of cages have meshes that are
more stretched out (Fig. 2).
Mesh size can be described in many ways. Bar length is
the distance between two knots while mesh size is the
Fig. 2. Hanging ratio and corresponding vertical mesh opening
Solidity is used to describe the ‘tightness’ of a net. This is
the ratio between the total area that the net covers,
compared to the area covered with threads including
knots. This relation is important when the resistance
Fig. 1. Mesh size
against water flow through the net is to be calculated.
27
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Fouling on the net will increase the solidity, because the
z
covered area is increased.
completely in water to form a diamond-shaped hole
so as to allow good water exchange with minimum
Mesh-size selection is dependent on the species and size
use of netting material
to be stocked. The seabass, having a more pointed snout
would require a cage of smaller mesh-size than would a
z
Meshes should not be large enough to gill the fish
stocked
grouper of the same size. The relationship between cage
mesh size and a few fish species are summarized in Table
z
2 and recommended material amd mesh size for different
Mesh size should be roughly equal to about 25% of
the body length of the fish
cage types are given in Table 3.
Construction of cages
Factors to be considered for mesh size selection
z
The meshes of the cage should remain open
Mesh size should not be less than 10 mm to assure
Hapa cages
good water circulation through the cage while holding
The dimensions of the hapa cage can range from 2×2×2
relatively small fingerlings (10 to 12.5 cm) at the start
m to 3×3×3 m to 5×5×2-3 m depending on the scale of
of the production cycle.
stocking. Mesh size can range from 8 mm to 9.5 mm
Table 2 Relationship between cage mesh size and fish species
Type of cage and
netting material
Mesh-size
(cm)
Grouper, TL
(cm)
(Epinephelus tauvina)
Seabass,
TL (cm)
(Lates calcarifer)
Snapper
TL (cm)
(Lutjanus johni)
5–10 10–15 15–40 40–50 50–75 75 and > 7.5–10 10–25 25–30
Broodstock
Broodstock
Hapa (PA 4 ply)
8
Nursery (PE 15 ply)
13
Production (PE 24 ply)
+
>30 5–10 10–15 15–2050 and >
Broodstock
+
+
+
+
25
+
25
+
50
+
+
+
+
+
75
+
+
+
+
100
+
(Source: FAO, 1988)
Table 3 Recommended material and mesh size specifications for different cage types
Cage
Recommended material specifications
Mesh Size
(mm)
Fish size recommended(TL, cm)
Grouper
Seabass
Hapa
Polyamide (nylon) 210D/2x21200 meshes deep.
9
5–10
10 and <
Nursery
Polyethylene, 380D/2x3300 meshes deep.
9.5
10–15
10–15
Polyethylene, 380D/3x3 or 5x3300 meshes deep.
12.7
10–15
10–15
Polyethylene, 380D/5x3 or 6x3300 meshes deep.
19.1
15–30
15–20
Grow-out
Polyethylene, 380D/6x3 or 7x3300 meshes deep.
25.4
15–40
20–30
Polyethylene, 380D/7x3 or 8x3300 meshes deep.
25.4
15 – 40
>30
Polyethylene, 380D/9x3300 meshes deep.
38.1
15–40
>30
Polyethylene, 380D/10x3 or 11x3300 meshes deep.
5.8
40–50
-
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
depending on the initial size of fry/fingerling stocked. The
z
The dimensions of the cage should be slightly smaller
hapa cage is usually constructed of knotless material, e.g.,
than the floating frame on which it is suspended so
PA, so as to avoid any abrasion to the fish fingerlings
that the cage fits well within the frame.
during hauling of the cage. Knotted netting should be
avoided as far as possible as the abrasions caused to the
z
the meshes required that would give the desired
fingerlings could result in disease, especially bacterial
vertical mesh opening or hanging. Stretching the
infection. Besides, small-mesh knotted netting materials
material to the actual cage dimension will result in
are also heavy and easily fouled as fouling organisms tend
uneven measurements and irregular fit.
to be congregated to the knots. Main rope is made from
PP/PE of 5–6 mm diameter. Bolch line is usually made of
Cutting: Synthetic nets are to be cut by calculating
z
Vertical mesh opening or hang-in of the netting must
PP/PE of 2 – 3 mm diameter. PA netting twine of 210D/
be pre-determined. The vertical mesh opening or hang-
9x3 is used for hitching the bolch line to the main rope,
in of the netting is defined as the mesh size of the
and 210D/6x3 is used for joining the netting material/
netting at free hanging and is expressed as a
panels/sections to the bolch line.
percentage.
Nursery cage
Like the hapa, the nursery cage can be of 2×2×2 m, or
3×3×3 m, or 5×5× 2-3 m, depending on the scale of
z
A vertical mesh opening or hanging of about 70 % is
recommended for cages as the mesh then approaches
that of a square as seen in Fig. 2.
stocking. The netting material used is usually of the
The side net panels are joined to the bottom panel by
knotted type. Polythylene (PE) is usually selected. Mesh
sewing with twine. Sewing is done by passing the twine
size can range from 9.5 mm (3/8") to 25.4 mm (1")
along the outer edges of the two panels in a 1 mesh side
depending on size and type of fish stocked. Main rope is
to 1 mesh bottom ratio. For every 5 stitches, an overhand
PP/PE of 8 mm diameter while bolch line is also PP/PE of
knot is made. A bolch line is to allow the attachment of
2mm diameter. PE twine of 380D/4x3 is used for joining
the main rope to the netting material. It is passed along
the netting panels and 380D/6x3 or 7x3 is used for joining
the 4 bottom seams of the cage between the side panels
the bolch line to the main rope.
and bottom panel (basal bolch) and along the top square
Grow-out cage
Cage dimensions of grow-out cages are similar to hapa and
nursery cages. Like the nursery cage, grow-out cages are
also constructed of knotted netting, usually of PE material.
of the side panels (top bolch). Threading is done through
each mesh, if necessary. The bolch line is a thin rope
whose diameter varies according to the netting material
used.
Mesh sizes start from 25.4 mm (1") and mesh size to be
The main rope is used for giving the cage its shape and
selected depends on the size of fish stocked. Larger sized
for suspending the cages. It is sewn on to the bolch line.
fish of 30 cm could be stocked in cages of mesh size 50.8
It is of a larger diameter than the bolch line and its size,
mm. The main rope is PE of diameter 10 mm. Bolch line, as
like the bolch line, varies according to the netting material
for nursery cages, is of PP/PE of 3 mm diameter.
used for the construction of the cage
Factors to be considered for cage construction
Maintenance of the cage
z
The net panels should be cut such that there is
The normal lifetime of a net bag will vary with the site
minimum wastage of netting material
conditions.. As a general rule, if the breaking strength of
29
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
the net bag below the surface falls below 65% of the initial
affected by salinity, water depth and substrate area and
strength it is considered as unserviceable. With proper
immersion period.
care, cleaning and repair, the economic life of
polyethylene nets ranged from two to five years. The small
mesh size net of less than 2.4 cm foul more rapidly and
has to be cleaned more frequently. In temperate regions,
the life time of a net bag is usually 5 years.
Biofouling
Biofouling is a major problem in cage culture during
summer months especially at marine sites. Biofouling
occurs as a result of the settlement and growth of
sedentary and semi-sedentary organisms like barnacles,
tunicates, tube worms, mussels, bryozoans and algae on
artificial structures placed in water. It mostly composed
of organisms with organic or mineral material trapped in
between. Floating cage culture using nets is particularly
Multifilament netting material is particularly vulnerable
to fouling, as it is non-toxic, contains many crevices that
can entrap and protect settling organisms, and has a high
surface-area to volume ratio. The materials used for
making the nets (metal, synthetic materials) and their
form (galvanized panels or nets) also affect fouling levels.
Galvanized panels developed much less fouling than the
synthetic fibre netting panels. Since fouling encrusts small
mesh nets more rapidly, the fish farmer should use the
largest mesh size permitted by the size of the fish. Netting
colour significantly affected the growth and composition
of algal fouling, but had no effect on invertebrate fouling.
Fouling Control
vulnerable during the hot season. Although biofouling of
The prevention of fouling on mariculture structures is
artificial substrates has been well studied, biofouling
complicated by the choice of net material and the dangers
pertaining to the aquaculture environment and biofouling
of toxins to cultured species. Antifouling practices include
on cages in tropical marine waters is less studied. The
predominantly the use of copper-based antifouling
frequent cleaning of nets is not only costly and labour
coatings. There have been incidents where antifouling has
intensive but often gives rise to loss of stocked fish due
adversely affected fish: in the 1980s, trials with tributyl-
to net changes and damage. Uncleaned nets on the other
tin on cages caused significant effects to farmed salmon.
hand can cause severe physical stress on the cage nettings
The antifouling solutions presently available are not ideal,
during strong current flow when they could tear. Fouling
and it is widely accepted that there is an urgent need for
significantly impedes the water flow and therefore the
research into anti-fouling technologies. Such alternatives
supply of dissolved oxygen to the caged fish. Fouled
include the adoption of “foul-release” technologies and
netting also increases structural fatigue on cages and the
“biological control” through the use of polyculture
fouling communities may harbour disease-causing
systems. However, none of these have, as yet, been
microorganisms. Hydrodynamic forces on a fouled net can
proven satisfactory. In view of current legislative trends
be 12.5 times that of a clean net. Concurrently, the weight
and the possible future “phasing out” of available
of cages can increase sever-fold, causing further structural
antifouling materials, there is a need to find alternative
stress as well as a reduction in cage buoyancy and
strategies. The use of most commercially available,
increased net deformation. Retarded water flow and
antifouling chemicals or coatings on cage nettings is
inorganic and organic enrichment through fish feeds and
largely restricted due to concern of environmental
faecal matter enhance the macrofouling assemblage on
toxicity. For these reasons, the natural control of
fish netting. The structure, colonization dynamics and
biofouling or environment-friendly methods is to be used.
depth distribution of the macrofouling assemblage are
Such methods require a better understanding of the
30
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
fouling community of cage netting, particularly how it
Cage cleaning: The nets should be cleaned regularly to
interacts with the physical environment and aquaculture
prevent excessive fouling that may result in net breakage
itself. It has been recently demonstrated that silicone
and heavy losses of fish. The smaller the mesh size, the
coatings provide an effective non-toxic solution to reduce
heavier the rate of fouling. Nets of mesh size less than
fouling on sea-cages and to increase the ease of fouling
2.5cm should be cleaned within 1 or 2 weeks of use
removal.
whereas the larger size nets need to be cleaned in 30 to
Fouling organisms of the cage can be controlled
biologically to some extent by using grazer fish species
90 days. Fouling organisms are removed by a high pressure
water jet.
within the culture fish. Grazing by wild fish and other
Cage drying: The cleaned net is checked for holes and
predators could also contribute to the slower colonization
repaired before it is used again. It can also be hung-up to
rates outside the cages. The introduction of predatory
dry and mend in position.
fishes or sea stars could provide some amount of control
on the growth of fouling organisms. Cyprinus carpio
consume algae on nets and in the cage. Thus polyculture,
when it is possible, may be a solution to limit fouling
development in some sites.
Cage mending: Net panels may get damaged or ropes may
become weakened from frequent use. Panel and roped
replacement or partial replacement with rejoining may
be required, in such cases.
Due consideration need to be given for the design,
Abrasion
construction and maintenance of the cage for the success
Abrasion of the netting with fishes, with the rafts and
of cage culture. Selection of suitable netting material,
frames as well as between inner and outer net in cases
fixing of optimum mesh size and periodic maintenance
where double netting is provided are problems
of the net bag are the most important parameters to be
encountered. It is a common practice to have double
taken into account. Focused research is needed on
netting. The outer one serving as a predator net, to protect
selection of netting materials, optimization of cage design
the inner net with the fish stock.
and construction for different species and culture sites
and on fouling control measures.
In cases where the netting has a chance of rubbing with
the frames or brackets, provision of a selvedge netting of
References
same mesh size but of thicker twine would avoid the
breakage of netting along the point of abrasion
Aqua Farm News, Vol X No.3 (May-June 1992), Bureau of
Fisheries and Aquaculture Resources (BFAR) Regional Office.
Maintenance procedure
Beveridge, M.C.M. 1987. Cage Aquaculture. Fishing News Books
Ltd. Farnham. Surrey. UK. 352 pp.
Maintenance of cages involves net changing, cleaning and
mending.
Cage changing: The frequency of change depends on the
mesh size of the cage and the season for fouling organisms
which cause the cage to clog. As cage changing is time
consuming and laborious, a mechanised net hauler may
be considered for lifting out heavily fouled cages.
FAO 1988. Training manual on marine finfish cage culture in
Singapore, FAO, Rome
FAO.1988. Seminar report on the status of marine finfish cage
culture in China, DPRK (Democratic People’s Republic of
Korea), Indonesia, ROK (Republic of Korea), Malaysia,
Philippines, Singapore and Thailand
Kawakami, T. 1964. The theory of designing and testing fishing
nets in model. In: Modern Fishing Gear of the World (H.
Kristjonsson, D.), Fishing News (Books) Ltd., London.
31
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Klust, G. 1973. Netting materials for fishing gear. FAO Fishing
Manuals, Fishing News (Books) Ltd, London, England, 173 p.
Lekang, O. Aquaculture Engineering, Blackwell Publishing Ltd.,
UK. 340p.
Milne, P.H. 1970. Fish farming: a guide to the design and
construction of et enclosures. Mar. Res. Bull. No. 1.
Department of Agriculture and Fisheries for Scotland.
Edinburgh
Nash, C.E. 1988. A global overview of aquaculture production.
J. World Aquacult. Sot., 19(2), 51-58
32
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Principles and practices of cage mooring
Boby Ignatius
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
bobycmfri@yahoo.co.in
Moorings are required to hold cages against the forces
Mooring requirements should be determined by the design
generated by wind, currents and waves and to allow the
and type of the cages and the characteristics of the site.
fish stocks and the cages and let the best chance of
It would first be necessary to quantify the incident forces
survival. In sheltered waters, requirements to moor a cage
that are likely to act on the cage under the worst possible
safely were minimal. This has changed dramatically with
weather conditions, and then to evaluate the proportion
moves into coastal waters, and a potentially much higher
of energy transferred to the mooring lines and anchors.
wave climate. Mooring failures were common place in the
Two types of analysis can be used: quasi static and
early days of coastal farming, but a better understanding
dynamic response. The loadings transferred to mooring
of the problems, and more sophisticated analysis has
lines vary enormously depending on current and wave
largely reduced these risks. Perhaps the most important
conditions, cage design and number of lines employed.
point is to view the cage group, its nets and moorings, as
a single system, whose components are mechanically
Mooring design for a specific cage system and site
linked. Their dynamic responses cannot be considered in
Wind and current forces are proportional to the square of
isolation, each component affecting the other. Cage and
the velocity. Thus an increase in current from 1 knot to 2
mooring design is “site specific”, and careful and combined
knots will generate 4 times the drag on a rigid submerged
choice of cage type, nets and most specifically moorings,
body. Wave forces are much more difficult to compute,
has a considerable bearing on the ability of fish stocks to
because the dynamic response of a system depends on
survive in major storms, on exposed sites.
so many factors. A change in the mooring system will
Most moorings systems consist of lines and anchors that
change the internal loads on the cage system. This is a
secure cages in a particular location. However, the
complex topic, but in general a mooring system should
moorings also influence the stress acting on cage
be designed not only for specific cages, but also for the
structural members and the behavior of the cages in rough
expected site conditions of water depth, wind, waves and
weather, and can affect production, profitability and staff
current.
safety. They are therefore an important - indeed, integral
part of the cage system and should be carefully designed.
Mooring components
Thus the collar, net and mooring components of a cage
Whichever type of mooring layout is employed, a number
system should be designed together, although in practice
of elements need to be assembled together, correctly
the cages are usually chosen or built first with the mooring
specified and installed, physically and operationally
system being designed as an afterthought.
compatible with each other, and effective in use and
33
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
maintenance. Key elements include the anchor or mooring
attached, so that they can be floated to the required
unit on the seabed, the rising line, which connects the
location at high tide. Once installed, they are difficult to
anchor to the surface system, and the surface or
recover.
subsurface mooring grid. The major elements comprise
several smaller sub-units – particularly links, shackles,
droppers, safety lines, buoys, etc., which in effect are
integral in the complete system.
There are numerous types of embedding anchor. The
holding power of an embedding anchor is related to its
frictional resistance in soil, and so is dependant on fluke
area, soil penetration and the mechanical properties of
Anchor specifications
the soil rather than simply the mass of the anchor.
A range of different types is available, commonly from
Embedding anchors are very efficient, i.e. they have a high
the shipping/fishing industry. Major options are usually
holding power to mass ratio. Under optimum conditions,
between gravity or dead weight devices – mooring blocks
they are 10-500 times as efficient as block anchors. They
or mass anchors, which rely primarily on their weight, and
are more expensive than block anchors in terms of cost
those which rely on their ability to wedge into the seabed
per unit holding power and have to be bedded in properly.
substrate. Blocks are widely used because of their
The use of two anchors connected together gives greater
simplicity, their stability to tension in all directions, and
holding power than the sum of independently moored
their relative ease of positioning and relaying, but their
anchors. There are numerous other type of anchor,
efficiency is low. Gripping devices are much lighter and
combining the properties of block and embedding types,
more efficient in the appropriate substrates – e.g., muds
while others are designed for particular types of substrate.
and shingle mixes, but need to be properly tensioned; once
bedded in they can also be difficult to reposition.
The simplest and cheapest type of marine anchor is the
dead weight or block anchor, which typically consists of
a bag of sand or stones or a block of concrete or scrap
metal. The holding coefficient of the anchor (k) is defined
as (R) the horizontal force divided by the mass of the
anchor. The holding coefficient (k) depends upon the angle
between the anchor and the cage and thus the ratio
between water depth and line length and the nature of
the substrate.
Prior to choosing or installing anchors it is advisable to
survey the sea bed. Anchors should be positioned first.
The position of the anchors can be accurately established
using a global positioning system or by taking bearings
with respect to local. Easily visible land marks.
Rising line components
A range of materials and configurations may be used, the
most common of which involves a chain section at the
lower end of the line, a synthetic rope in the main upper
length, and various elements of buoyancy or weighting
Block anchors have low holding power per unit-installed
to adjust the profile of the line, and its response geometry
weight. The performance of a sand bag anchor is much
when subject to varying load. A range of different types
poorer in mud. Concrete block anchors may be simply
and specifications may be available for chain and rope.
fabricated using wooden shuttering, tyres or any other
Key issues concern weight and tensile strength, elasticity
convenient object as mould. Steel rods for strengthening
(length change with applied tension), stretching,
and eyebolt for a mooring attachment are usually
dimensional wear, degradation. Float units need to be
incorporated. Once fabricated, the blocks can be
specified according to volume and shape, and to their
transported to the waters edge at low tide and floats
resistance to deformation when submerged.
34
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Mooring lines must perform two functions: they must
The total length of the mooring line should be at least
withstand and transmit forces. The loads imposed on a cage
three times the maximum depth of water at the site and
mooring system are principally dynamic. It is important that
where the rope joins the chain, a galvanized heavy duty
mooring lines have a high breaking strength and can absorb
thimble should be spliced into the rope and a galvanized
much of the kinetic energy of rapidly changing force s,
shackle of the appropriate size should be used to connect
otherwise theses forces will be transmitted directly to the
the chain and tot eh rope.
anchors. Natural fibre rope is not suitable as it is easily
abraded and prone to rotting. Steel cable, although
immensely strong, is expensive and heavy. Chain is
extremely strong but again is heavy and is usually used in
conjunction with synthetic fiber rope. Synthetic ropes of
same diameter nylon and PES are considerably heavier than
PP or PES. However, nylon is much stronger on a per unit
weight or equivalent diameter basis than ropes fabricated
from the other materials. Braided ropes are lighter than
laid ropes and are generally weak. They also cost more and
have few advantages other than they are easier and more
pleasant to handle and do not kink. Although it can cost
twice as much as PE or PP rope of equivalent strength,
nylon has high extensibility and thus energy absorbing
properties, an important factor in designing cage moorings.
Ropes should not be attached directly to either shore or
sea anchors, but instead should be connected via a section
of chain. The chain serves to increase the effectiveness
of the mooring system, which directly act as an efficient
type of anchor and improves the holding power of existing
anchor by both reducing the angle between the mooring
line and anchor and by increasing energy absorbing
properties of the mooring line.
An alternative mooring line composed mainly of chain is
occasionally employed. Typically 12-25mm chain, two or
three times the maximum depth of water in length is
connected from the anchor to a float positioned 10m or
so from the cage and a section of rope –PES or nylonused to link the floats to the cages. The buoy minimizes
the vertical loading on the cages and must be sufficiently
large to support the mass of the chain in the water and to
resist the vertical forces imposed by the cages on the
mooring system. A single float per mooring line tends to
be used, although reductions in line tension from using a
series of floats with the same floatation capacity as a
single float. Under shock loads, the chain/buoy acts as a
spring absorbing much of the energy that would otherwise
be transmitted to the anchor.
Two types of mooring systems be used: multiple and
single point. The former is more common and involves
securing the cages in one particular orientation while
with the latter the cage are moored from one point only,
allowing them to move in complete circle. Single point
moorings tend to be used with rigid collar designs in
sheltered sites. They use less chain and cable than
multiple point moorings and because they adopt a
Moreover, a section of chain is necessary at the anchor
position of least resistance to the prevailing wind, wave
since it is much resistant than synthetic fibre rope to the
and current forces, both inter cage forces and torsion
prevailing high abrasion forces. There are several types of
forces at linkages are reduced. Single point mooring
chains are available. Wrought iron is very variable in
systems also reduce the enormous net deformation seen
quality; the best has excellent corrosion resistance while
in conventional mooring systems and have been used
the poorer grades are inferior in all respects. Mild steel
with successes to moor large offshore cages. Cages
chain, with low carbon and manganese contents has been
moored from a single point also distributes wastes over
widely recommended for cage anchorages. A fairly heavy
considerably larger areas than those secured by a
grade of chain is recommended.
multiple point system.
35
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
The orientation of cages with multiple moorings depends
one structural member to another, are frequently used.
upon the nature of the site and upon the type and group
Anchors are deployed to resist the principal directions of
configuration of the cages. If particularly exposed or if
force and sometimes may be used installed on shore as
currents are strong, then it may be best to secure cages
well as at sea. Mooring lines must be secured to cage
in the position of least resistance to the prevailing wind
collars via attachment points able to withstand the forces
and current forces. Where a site is sheltered and water
generated. Structural members should be used and where
circulation is poor, it may be better to moor cages so that
abrasion is expected the line should be protected by
water exchange is maximized. However, there may be
encasing in plastic pipe.
restrictions on mooring orientation imposed by the site
size or by suitability of mooring grounds.
The number of mooring lines used determines the
distribution of forces to the anchors. Most methods of
mooring involve the use of ropes and chain to link the
cage or cage group to anchors or pegs secured to the sea
Installation methods
The installation of mooring systems is an important aspect
of the overall development of a cage site, and requires to
be planned with care.
(i)
Working base: a suitable and secure area for storing
bed. The mooring line is often termed as a ‘riser’. Although
and laying out the mooring components needs to
this is most common system there are alternatives. Some
be identified – ideally a level, surfaced area.
cages may use a submerged rope or cable based mooring
grid, to which cages may be attached temporarily using
(ii)
and positioning the mooring components and
near horizontal lines. One further alternative is to drive
operating in the expected site conditions
long posts into substrate and to attach cage directly either
with ropes or with metal hoops or tyres that permit some
Workboat or mooring vessel: capable of moving
(iii)
Cranes: dockside and on mooring vessels – capable
vertical tidal and wave induced movement. In theory the
of lifting and moving the mooring elements safely
number and dimensions of posts required and the depth
at the required horizontal reach.
to which they must be buried could be computed from
the estimates of the forces acting on the cage system
(iv)
areas, for mooring components to be taken safely
and data on the soil characteristics, but in practices it is
to the intended cage site.
determined by experience. Although sometimes employed
in sheltered and shallow inland and coastal sites with
Access: – for materials to be taken to the assembly
(iv)
Marking out: key locations in the mooring site can
suitable substrates, this method of mooring is not widely
be marked out on a hydrographic chart, checked
used.
on site with GPS or conventional optical surveys;
local transect markers can be identified, and
There are a variety of methods of using single and multiple
temporary positions marked with light lines and
point moorings. one or two heavy ground chains can be
floats
laid which connects the cages to the anchors via mooring
lines. Alternatively mooring lines can be run directly from
(v)
Making up moorings: the mooring lines and grids
the cages to the anchors. Points of stress are formed
need to be adjusted to length and assembled to
where mooring lines are secured to the cages and so it is
form the appropriate sub-components, which
important that they are secured at a number of places.
would then be finally linked together on site once
Joints, where stress accumulate or are transferred from
the anchors are laid. Primary work can most easily
36
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
(vi)
be done on shore, using temporary measure lines
Mooring maintenance
or markers to help lay off the line lengths. Further
Cage moorings are a dynamic system, which must respond
adjustments can be done at sea, and all
to motion, under load, every minute of the years it is
components and connections given a final check
installed. Maintenance is critical, to ensure that
before installation
components are physically sound and that linkages are
Laying anchors and risers: if blocks are used, these
can be set at the intended site, using positioning
co-ordinates to define the location. For embedding
anchors, these should be dropped a suitable
checked periodically, bolts and shackle pins need to be
tightened, and riser lines may need to be adjusted.
With a rigorous and effective system of maintenance of
tension) from the place of intended location, and
both cages and moorings, with clearly defined parameters
tensioned inwards to their final position. Laying
for replacement or repair, a well designed and installed
of moorings and lines should be done carefully,
system should be capable of reliable and secure operation.
line, to tangle or snag the line, or to endanger staff.
(x)
chain links, brackets, shackles, splicing eyes, need to be
distance outwards (i.e., opposite the direction of
taking particular care not to foul anchors with riser
(ix)
secure. Critical dimensions of items subject to wear –
Mooring systems must be checked at regular intervals
and fouling removed from buoys and mooring lines. it is
Tensioning the rising lines: these need to be finally
essential that any mooring inspection assesses
adjusted to ensure that the cage and/or mooring
component strength to see if it deviates significantly from
assembly is correctly and evenly tensioned around
design strength and that it should also assess likely
its axes.
deterioration in the interval to the next inspection.
Diver swim of rising lines: finally, it is very
Reference
important to check the whole system visually –
to ensure that blocks or anchors are cleanly placed
and/or embedded, that lines are lying properly and
are not kinked or tangled, and that connections
are sound.
Beveridge, M.C.M.B., 1996. Cage Aquaculture 2nd Edn. Fishing
News Books, Oxford, p. 346.
Turner R, 2000. Offshore mariculture: Mooring system design.
In Muir J. (ed.), Basurco B. (ed.) Mediterranean offshore
mariculture. Zaragoza: CIHEAM-IAMZ, p. 159-172.
37
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Taxonomy, identification and biology of
Seabass (Lates calcarifer)
Grace Mathew
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
gracejacob1985@yahoo.com
Introduction
female fish provides plenty of material for hatchery
Lates calcarifer (Bloch), commonly known as giant sea perch
production of seed. Hatchery production of seed is relatively
or Asian seabass, is an economically important food fish in
simple. Seabass feed well on pelleted diets, and juveniles
the tropical and subtropical regions in the Asia –Pacific.
are easy to wean to pellets. Seabass grow rapidly, reaching
They are medium to large-sized bottom-living fishes
a harvestable size (350 g – 3 kg) in six months to two years.
occurring in coastal seas, estuaries and lagoons in depths
between 10 and 50m. They are highly esteemed food and
sport fishes taken mainly by artisanal fishermen. Because
of its relatively high market value, it has become an
attractive commodity of both large to small-scale
aquaculture enterprises. It is important as a commercial
Today Seabass is farmed throughout most of its range, with
most production in Southeast Asia, generally from small
coastal cage farms. Often these farms will culture a mixture
of species, including Seabass, groupers (Family Serranidae,
Subfamily Epinephelinae) and snappers (Family Lutjanidae).
and subsistence food fish but also is a game fish. The most
Australia is experiencing the development of large-scale
important commercial fish of Australia, and the most
seabass farms, where seabass farming is undertaken
sought after game fish, generates millions of dollars per
outside the tropics and recirculation production systems
year in revenue for the sport fishing. Lates calcarifer, known
are often used (e.g. in southern Australia and in the north-
as seabass in Asia and barramundi in Australia, is a
eastern United States of America). Seabass has been
euryhaline member of the family Centropomidae that is
introduced for aquaculture purposes to Iran, Guam, French
widely distributed in the Indo-West Pacific region from the
Polynesia, the United States of America (Hawaii,
Arabian Gulf to China, Taiwan Province of China, Papua
Massachusetts) and Israel.
New Guinea and northern Australia. Aquaculture of this
species commenced in the 1970s in Thailand, and rapidly
spread throughout much of Southeast Asia.
Among the attributes that make seabass an ideal
candidate for aquaculture are:
It is a relatively hardy species that tolerates crowding and
has wide physiological tolerances. The high fecundity of
Taxonomy
Phylum
Sub-phylum
Class
Sub-class
Order
Family
Genus
Species
Chordata
Vertebrata
Pisces
Teleostomi
Percomorphi
Centropomidae
Lates
Lates calcarifer (Bloch)
38
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
The above is an accepted taxonomic classification of
edge of pre-operculum is with strong spine; operculum
seabass or giant perch. Seabass has been placed under
with a small spine and with a serrated flap above original
several families by various authors in the past (e.g. the
of lateral line. Dorsal fin with 7 to 9 spines and 10 to 11
grouper family, Serranidae and family Latidae, etc.)
soft rays; a very deep notch almost dividing spiny from
However, Centropomidae is the commonly accepted
soft part of fin; pectoral fin short and rounded; several
family name of this species, and the recognized generic
short, strong serrations above its base; dorsal and anal
name is Lates. Other names such as Perca, Pseudolates,
fins both have scaly sheath. Anal fin round, with three
Holocentrus, Coins, Plectropoma, Latris , and
spines and 7–8 soft rays; caudal fin rounded. Scale large
Pleotopomus were also given by various authors who
ctenoid (rough to touch). Colour: two phases, either olive
collected the fish specimens from different areas. Bloch
brown above with silver sides and belly in marine
(Schneider 1801) stated that Lates calcarifer occured in
environment or golden brown in freshwater environment.
Japan Sea but named it as Holocentrus calcarifer.
In adult, it is usually blue-green or greyish above and silver
English: Asian seabass, Barramundi perch; French: Brochet
de mer.
below. Fins are blackish or dusky brown. Juveniles have
mottled pattern of brown with three white stripes on head
and nape, and white blotches irregularly placed on back.
The common local names of this species are listed below:
Eyes are bright pink, glowing at night.
English
:
Giant perch, white seabass, silver seaperch,
giant perch, palmer, cock-up seabass
Distribution
India
:
Begti, bekti, dangara, voliji, fitadar, todah
East Bengal
:
Kora, baor
Sri Lanka
:
Modha koliya, keduwa
areas of the Western and Central Pacific and Indian
Thailand
:
Pla kapong kao, pla kapong
Ocean, between longitude 50°E - 160°W latitude 24°N –
Malaysia
:
Saikap, kakap
25°S (Fig. 1). It occurs throughout the northern part of
North Borneo
:
Ikan, salung-sung
Asia, southward to Queensland (Australia), westward to
Vietnam
:
Ca-chem, cavuot
East Africa. Found in coastal waters, estuaries and
Kampuchea
:
Tvey spong
lagoons. Usually occurs at depths of 10 to 40m.
Philippines
:
Kakap, apahap, bulgan, salongsong,
katuyot, matang pusa
Indonesia
:
Kakap, pelak, petcham, telap
:
Barramundi
Geographic distribution
Seabass is widely distributed in tropical and sub-tropical
Australia and
Papua New
Guinea
Morphology and distinctive characters
\Body elongated, compressed, with deep caudal peduncle.
Body large, elongate and stout, with pronounced concave
dorsal profile in head and a prominent snout; concave
dorsal profile becoming convex in front of dorsal fin.
Mouth is large, slightly oblique, upper jaw reaching to
behind eye; teeth villiform, no canine teeth present. Lower
Fig. 1 Geographic distribution of Lates calcarifer (FAO, 1974)
39
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Ecological distribution
been recorded in the Indo-Australian region (Weber and
Seabass is a euryhaline and catadromous species; inhabit
Beaufort 1936).
freshwater, brackish and marine habitats including
streams, lakes, billabongs, estuaries and coastal waters.
Sexually mature fish are found in the river mouths, lakes
or lagoons where the salinity and depth range between
30–32 ppt and 10–15m, respectively. The newly-hatched
larvae (15–20 days old or 0.4–0.7cm) are distributed along
the coastline of brackishwater estuaries while the 1-cm
size larvae can be found in freshwater bodies e.g. rice
fields, lakes, etc. (Bhatia and Kungvankij, 1971). Under
natural condition, seabass grows in fresh water and
migrates to more saline water for spawning. Adults and
Eggs are pelagic, hatch within 24 hours, and the larvae
grow quickly as they move into mangrove areas, mudflats,
and floodplain lagoons. Juveniles move into coastal waters
after one year, and then migrate upstream where adults
reside for three to four years. Populations landlocked by
dams migrate to the dam face, but do not spawn. It is
reared extensively by aquaculture as food or for game fishstocking programs. Catadromous migration is observed,
where the fish migrates downstream to shallow mudflats
in estuaries during the wet season.
juveniles tend to be solitary, patrol home ranges near
structure, and may be territorial. Migration is seasonal.
Life history
Seabass spends most of its growing period (2–3 years) in
freshwater bodies such as rivers and lakes which are
connected to the sea. It has a rapid growth rate, often
attaining a size of 3–5 kg within 2–3 years. Adult fish
(3–4 years) migrate towards the mouth of the river from
inland waters into the sea where the salinity ranges
between 30–32 ppt for gonadal maturation and
subsequent spawning. The fish spawns according to the
lunar cycle (usually at the onset of the new moon or the
Fig. 2 Migration pattern of Lates calcarifer Bloch
Feeding habits
full moon) during late evening (1800–2000 hours) usually
Seabass or barramundi are opportunistic predators;
in synchrony with the incoming tide. This allows the eggs
crustaceans and fish predominate in the diet of adults.
and the hatchlings to drift into estuaries. Here, larval
Although the adult seabass is regarded as a voracious
development takes place after which they migrate further
carnivore, juveniles are omnivores. The fish is skilled at
upstream to grow. At present, it is not known whether
stalking or ambushing prey. Analysis of stomach content
the spent fish migrates upstream or spends the rest of its
of wild specimens (1–10 cm) show that about 20%
life in the marine environment.
consists plankton, primarily diatom and algae and the rest
are made up to small shrimp, fish, etc. (Kungvankij 1971).
Smith (1965) noted that some fish spend their whole life
Fish of more than 20 cm, the stomach content consists
in freshwater environment where they grow to a length
of 100% animal prey: 70% crustaceans (such as shrimp
of 65 cm and with 19.8 kg body weight. The gonads of
and small crab) and 30% small fishes. The fish species
such fish are usually undeveloped. In the marine
found in the guts at this stage are mainly slipmouths or
environment, seabass attaining a length of 1.7 m have
pony fish (Leiognatus sp.) and mullets (Mugil sp).
40
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
February to March. Spawning seasonality varies within
Sex determination
Identification of the sexes is difficult except during the
spawning season. There are some dimorphic characters
that are indicative of sex (Fig. 3).
the range of this species. Barramundi in northern Australia
spawn between September and March, with latitudinal
variation in spawning season, presumably in response to
varying water temperatures. In the Philippines barramundi
Snout of the male fish can be slightly curved while
spawn from late June to late October, while in Thailand
that of the female is straight.
spawning is associated with the monsoon season, with
z
The male has a more slender body than the female.
two peaks during the northeast monsoon (August –
z
Weight of the female is heavier than males of the same
z
October) and the southwest monsoon (February – June).
size.
z
The scales near the cloaca of the males are thicker
than the female during the spawning season.
z
During the spawning season, abdomen of the female
is relatively more bulging than the males.
Sexual maturity
In the early life stages (1.5–2.5 kg body weight) majority
of the seabass appear to be male but when they attain a
body weight of 4–6 kg majority become female. After
culture period of 3–4 years, however, in the same age group
of seabass both sexes can be found and identified as
mentioned above. In a fully mature female, the diameter
of the oocysts usually ranges from 0.4 to 0.5 mm.
Fig. 3 Photograph of adult male and female seabass
Spawning occurs near river mouths, in the lower reaches
of estuaries, or around coastal headlands. Barramundi
spawn after the full and new moons during the spawning
season, and spawning activity is usually associated with
incoming tides that apparently assist transport of eggs
Fecundity and spawning
and larvae into the estuary.
Females are larger than males, are highly fecund, and may
Seabass being highly fecund; a single female (120 cm TL)
be courted by one or more males at the same time. The
may produce 30–40 million eggs. Consequently, only
fecundity of seabass is related to the size and weight of
small numbers of broodstock are necessary to provide
the fish Spawning occurs between September and March,
adequate numbers of larvae for large-scale hatchery
with peaks in November to December and again in
production.
Table 1 Relationship between size of fish and number of eggs from the gonads of seabass (Lates calcarifer Bloch) (After Wongsomnuk
and Maneewongsa, 1976)
Total length(cm)
Weight
No. of fish
Range
70 – 75
76 – 80
81 – 85
86 – 90
91 – 95
5.5
8.1
9.1
10.5
11.0
3
5
4
3
3
Fecundity (million eggs)
Average
2.7 – 3.3
2.1 – 3.8
5.8 – 8.1
7.9 – 8.3
4.8 – 7.1
3.1
3.2
7.2
8.1
5.9
41
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Based on studies of spawning activity under tank
years of age (60–70 cm TL) when they reach sexual
conditions, mature male and female fish separate from
maturity as males, and then move downstream during
the school and cease feeding about a week prior to
the breeding season to participate in spawning.
spawning. As the female attains full maturity, there is an
increase in play activity with the male. The ripe male and
female, then swim together more frequently near the
water surface, as spawning time approaches. The fish
spawns repeatedly in batches for 7 days. Spawning occurs
during late evening (1800- 2200 hours).
Embryonic development
First cleavage occurs 35 minutes after fertilization. Cell
division continues every 15 to 25 minutes and the egg
develop to the multi-celled stage within 3 hours. Its
development passes through the usual stages: blastula,
gastrula, neurola and embryonic stages. Embryonic hear
starts to function in about 15 hours and hatching takes
place about 18 hours after fertilization at temperatures
of 28–30°C and salinities of 30–32 ppt (Table 2, Fig
Because they are euryhaline, they can be cultured in a
range of salinities, from fresh to seawater. When they
are six–eight years old (85–100 cm TL), seabass change
sex to female and remain female for the rest of
their lives. Sex change in Asian populations of this
species is less well defined and primary females are
common.
Although seabass have been recorded as undertaking
extensive movements between river systems, most of
them remain in their original river system and move only
short distances. This limited exchange of individuals
between river systems is one factor that has contributed
to the development of genetically distinct groups of
barramundi in northern Australia, where there are six
recognised genetic.
4a & b).
Larvae
Table 2 Embryonic development of seabass eggs (Kungvankij
1981).
Newly-hatched larvae have total length ranging from 1.21
Embryonic stage
to 1.65 mm averaging 1.49 mm. The average yolk sac
length is 0.86 mm. One oil globule is located at the
anterior part of the yolk sac which causes the hatchling
to float almost vertically or about 45° from its usual
horizontal position. Initial pigmentation is not uniform;
the eyes, digestive tract, cloaca and caudal fin are
transparent. Three days after hatching, most of the yolk
sac is absorbed and the oil globule diminishes to a
negligible size. At this stage, the mouth opens and the
Hours & minutes after spawning
Hours
Minutes
Fertilization
-
5
2-cell
-
35
4-cell
-
55
8-cell
1
10
16-cell
1
30
32-cell
1
50
64-cell
2
20
122-cell
3
-
Blastula stage
5
3
jaw begins to move as the larva starts to feed.
Gastrula stage
7
00
Larvae recruit into estuarine nursery swamps where they
Neurola stage
9
10
remain for several months before they move out into the
Embryonic stage
11
50
freshwater reaches of coastal rivers and creeks. Juveniles
Heart functioning
15
30
remain in freshwater habitats until they are three–four
Hatch out
18
-
42
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
There are at least two pigmentation stages in seabass
larvae. At 10–12 days after hatching, the pigmentation
of larvae appears dark gray or black. The second stage
occurs between 25–30 days old where the larvae develop
into fry. In this stage, the pigmentation changes to a
silvery-coloration.
It has been observed that only healthy fry of this stage
(20–30 days) swim actively. They are always lighter in color.
Unhealthy post larvae have dark or black body coloration.
Growth
The growth rate of seabass follows the normal sigmoid
curve. It is slow during the initial stages but becomes
more rapid when the fish attains 20–30 gm (Table 3).
Fig 4a Development of egg
It slows down again when the fish is about 4 kg in
weight.
Table 3 Age, average body length and weight of seabass under
tank conditions
Age(days)
Average
length(mm)
Average body
weight
Fertilized eggs
0.91
0
1.49
1
2.20
7
3.61
14
4.35
20
9.45
30
13.12
0.1
40
17.36
0.5
50
28.92
Conservation status
Not listed by the IUCN, but has been threatened by
Fig 4b Development of egg
habitat destruction and over fishing.
43
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Nursery rearing of seabass fry and
importance of grading and seed
transportation
Shoji Joseph
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
sjben@yahoo.com
The Asian seabass (Lates calcarifer) is an important food
that affect the survival rate of seabass larvae as well as
fish and a potential aquaculture species in tropical
juveniles. In case of inadequate feeding times not only
countries. It exhibits catadromous habits within its areas
the lack of food but also the cannibalism will work
of distribution. It is an advantageous culture species
together and the survival rate will be lower in double
because after early larval rearing in seawater, it can be
effects. The larvae or juveniles cannot survive if there is
cultured in all levels of salinity, from fresh to seawater,
inadequate supply of food, which comprises various live
and in a variety of culture systems from open ponds and
organisms, and that again varies with the development
cages to flow-through and closed recirculation systems.
of the larvae. Most of the food that seabass larvae feed
In addition, this species produces large number of eggs
on is composed of live zooplankton. The larvae first begin
that can be reared intensively on fresh and pelleted feeds,
to feed on rotifer. It is reported that other kinds of food
and can reach a market size of 350 to 700 g in one year or
have also been tried with the early larvae but without
less periods under optimum culture conditions.
success. The supply of live zooplankton is expensive and
Seabass spawn naturally in captivity and the fertilized
eggs take 12 to 15 hours for hatching. The spherical eggs
range from 0.74 to 0.80 cm in diameter with a single oil
globule from 0.20–0.28 mm in diameter (Maneewong and
Watanabe, 1984). The mouth opens when the larvae get
to about three days old and the yolk has been almost
completely absorbed. This is a sign that the fry can start
to feed.
Seabass larvae and juveniles
sometimes causes problems because zooplankton culture
needs time, facilities and skills. Further, the different kinds
of live food required must be prepared in time to satisfy
the need of the fast-growing larvae. To maintain a high
survival rate, the feeding schedule for the larvae must be
closely adhered to.
Nursery Management
Tank
Seabass fry and fingerlings should be reared in concrete
Seabass is a carnivorous voracious feeder; and it is highly
tanks up to the size 2.5 cm or 1 inch. After that, they can
cannibalistic in the earlier stages like larvae and juveniles.
be transferred for rearing in nylon net cages until they
Food and feeding are two of the most important factors
attain 25 cm or 10 inches in about 2 to 3 months of culture
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
period. The rearing tank should be cleaned up every time
(iii) the replacement may be gradual, occurring over several
before using. The rates of water replacement in the rearing
days, as in the culture of red sea bream and Japanese
tanks depend on feeding period of each age stage. In the
flounder. On 25th day, when the fry measures @1.0 cm, it
period of rotifer feeding to prevent the loss of rotifer
should be transferred to nursery tanks in the hatchery or
through the outlet, approximately 10–20 percent of the
nursery hapas at the farm site for weaning. Though seabass
water in the rearing tank is drained out only for the
prefers live fish food it could be weaned to trash fish within
replacement of rotifer supply each day. During Artemia
5-7 days. Fry are stocked @ 1000 nos./m3 in 4-5 tonne
feeding period, approximately 50 percent of water is
capacity tanks. The cooked and minced fish meat, made
changed while almost complete change is made during
into small pieces of 1.5- 2.5 mm, should be given as feed
trash fish feeding period. The sediment of dead organisms,
ad libitum during the nursery rearing. Grading (removal of
larvae or leftover food is siphoned out everyday. The
shooter fish) should be done on alternative days to reduce
management of seabass nursery is shown in Fig.1.
cannibalism.
1.__________3.__________10.__________14.__________20.__________25.__________30.__________40
2.__green water and other algae__
_________Rotifer _______
___________________Artemia_______
______Daphnia__________
_______Trash fish_________
3.——RCW——10-20% change———I————————50%——————————I——80%—————
4. ___________1st grading____I_________2nd grading___I______Weeky once_______
Fig. 1. Management method for seabass nursery tank within the first 40-day period 1 Time duration 2 Feed 3 Water change 4 Grading.
Weaning
Importance of grading and grading techniques
The inclusion of artificial food in the diet of marine fish
Cannibalistic behaviour of seabass fry can be observed
larvae is a critical stage in intensive larval rearing. The
after the fry completes metamorphosis, when they are
process of changing diet of the fish larvae from the live
about 15 days old (15 mm in total length). To maintain a
feeds to the artificial diets or vise versa is called weaning.
uniform size and minimize the mortality of the fry, grading
Weaning reduces the dependence on live feeds, and
of fry to size groups at regular and frequent intervals must
therefore reduces hatchery running costs. Person-Le Ruyet
be done. Due to cannibalistic nature of the fish, size
(1991) described three weaning strategies which have been
selection or grading or sorting of the larvae is of prime
applied to different species of marine fish larvae, with
importance based on the size of the fish. The first sorting
different levels of success; (i) weaning at first feeding has
should start at the second week since during this period;
been achieved with plaice and sole with lower survival than
the bigger fish can eat the smaller ones. After the first
achieved with live feeds; (ii) larvae may be reared for some
size grading at around 12-15 days old, size grading should
time on live feed, which is then replaced abruptly with
be done every 3-5 days (Maneswongsa, 1986; Ruangpanit,
artificial feed; this strategy is used for European seabass or
1988). The easiest way of sorting is to use screen with
45
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
various mesh size so that the various sizes of fish can be
the water bodies. The net cages usually uses are 2x1x1.5
separated easily. Another material usually used for grading
m and they are usually set in open waters one day before
consists of plastic containers punched at the bottom with
stocking to remove the contaminants if any. Stock of
holes of 2, 3.5, 5, 6 and 7 mm in diameter. Fish are placed
2,000–3,000 fry are raised to the fingerling size in these
in the plastic containers which are floated in the newly
cages.
prepared larvae nursing tank. The small fish can pass
through the hole to the new tank. The remaining fish in
Survival Rate
the plastic containers are transferred into another tank
The system of culture outlined above gives about 85
and likewise graded with the use of a plastic container
percent hatching rate and a survival rate of 1–7 days old
with larger holes. Different types of graders fixed as well
larvae of 30 percent. For 8–15 days old larvae the survival
as adjustable types are now available in the international
is 80 percent, after which they can be maintained
market and a few types in the Indian markets.
indefinitely with negligible mortality (Table 1).
Stocking same size fish will reduce the rate of cannibalism,
Table 1 Survival rates of seabass larvae at various ages under
normal stocking rates in tanks
thus the survival rate can be increased and the growth
rate of the fish could also be faster and more uniform.
Age (days)
No. of larvae* per liter
Survival Rate(%)
1–7
30–40
37.2
voracious carnivorous feeders and the competition for
8–15
15–20
80.9
16–23
5–10
70.0
food is very high during the feeding time. If the number
24–30
2–5
85.3
Grading is also important in the fact that these fishes are
of fishes in the tanks as well as in the hapa are high, the
competition again increases and only the fittest will get
the food. Again these are column feeder and usually they
* Normal stocking density used in nursery tanks.
Salinity acclimatization
never feed on the left over food in the bottom. So all of
It is a euryhaline species except in its early larval stages.
them will have to get the food and eat in the same time,
These can be easily acclimatized from one salinity to any
this will not be possible in the tanks or hapa. Here the
other salinity i.e. from sea water to fresh water within
weak ones cannot grasp food as efficient as the healthier
short period of time without any mortality. Thus, it is an
ones and hence they become more weak when compared
advantageous culture as it can be cultured in all levels of
to the eating ones that grow further in size.
salinity, from fresh water to sea water, and in a variety of
culture systems from open ponds and cages to flow-
Growth and care of larvae as they develop to fry and
through and closed recirculation systems. It can easily
Juveniles
adjust to change of 5 – 10 ppm at a time. Therefore in a
When the fry are 50 days old or 1.0-2.0 cm length they
day it can be changed from sea water to fresh water and
are transferred to another tank (Ruangpanit et al., 1988).
vise versa.
The ground fish meat can be fed at age 45 days with
Artemia nauplii. Filtered sea water is totally changed and
Collection and conditioning of fry before transport
supplied every day. The semi moist compound diet is given
Fry are collected from the rearing tanks and placed in
three times a day. The juveniles can also rear in the net
smaller receptacles. Fry are treated with 5 ppm of
cages in the open waters. They can be moved from the
acriflavine solution or 0.5 ppm of copper sulfate solution
rearing tanks for culture in net cages of different size and
for 5–10 minutes. There should be no feeding within 1–2
shape according to the convenience and availability of
hours before packing.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Packing
is advantageous than other methods since it can be easily
Plastic bags of 40 × 60 cm of proper gauge are filled with
6–7 litres of fresh seawater and saturated with oxygen;
10–12 litres of oxygen gas are used for packing. The
amount of transportable fry depends on size of fry, water
temperature in plastic bags and duration of travel and
handling from source of fry to its destination.
managed and installation of rearing facility requires less
space and capital investment. The infrastructural facilities
including the man power is very less compared to the
tank systems. The huge amount of water exchange can
be avoided if it is reared in hapa in the ponds. It is easy to
maintain the water quality parameters in the ponds if it
is having easy approach to the natural water bodies. If
Transport
the ponds are provided with the water exchange facility
In transporting by truck, a mixture of crushed ice and
it is well and good. The ponds with tidal fled systems are
sawdust is needed to control the water temperature in
very good as the water can be entered and removed easily
the plastic bags during transport. The mixture is spread
without any power consumption. Again the number of
uniformly on the floor of the truck before the plastic bags
the hapa can be extended to any scale depending on the
are laid upon it. The proportion of crushed ice and sawdust
necessity and the capability of the farmer. It can be
is 1:1 for long—period transport (12–16 hours) and 1:2 for
maintained in a corner of the grow-out pond or near the
short periods (4–5 hours). Transportation should be carried
grow-out cages itself. The water flow in the cage site
out at night time. By this method, it is possible to control
washes away the metabolites and excess uneaten feed.
the water temperature between 19–23° C.
Pond preparation
The pond is made ready three weeks ahead of the date on
which the fry is expected. Adequate provision of water
inlet and outlet should be provided. A slope towards the
drainage side is preferred for the easy removal of the waste
materials for keeping good water quality in and around
the hapa. Both sluices/ the inlet and outlet channels
should be guarded by 1 mm mesh nets to prevent the
entry of unwanted fishes as well as escape of the fry in
the case of some hapa damage. The nursery pond should
be free from predators. Predators are killed by mahua
Fig. 2 shows the observed fluctuation in temperature of the
water in the plastic bags during transport. It was also
observed that the dissolved oxygen starting initially at 5.3 to
5.0 ppm will drop to 2.3-2.6 ppm at destination.
Pond nursery
oilcake (which is toxic for three weeks), which then acts
as a good fertilizer, giving a rich crop of zooplankton which
is good for the juveniles in rearing ponds. If there are no
weeds, to kill predators and competitors quickly, just add
100 kg of urea followed 24 hours later by 200 kg of fresh
Nursery rearing of seabass fry in ponds in hapa to the size
bleaching powder (which is toxic for only a week) for a 1-
of stocking is essential before release into the cages.
ha area of a 1-m deep pond. Fish killed in this way is
Nursery ponds may range in size from 500-2000 m . A
edible. A week after treatment with bleaching powder,
water depth of 1-1.5 m is desirable. Rearing of juveniles
add fresh cow dung (2,500 kg/ha) or a mixture of cow
in hapa in the earthen ponds is easy and economical when
dung (2,500 kg/ha) and poultry manure (1,250 kg/ha). If
it compared with that of the tank systems. This method
mahua oilcake is used, fertilizer need not be added for
2
47
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
the first 15 days. The pond should be stocked as soon as
The mesh size as well as the size of the hapa can be
it is ready and as early in the season as possible to get
changed as the fishes grow to bigger sizes which will
fry, which makes the best use of the available water and
increase the growth and at the same time reduces the
the high temperatures.
clogging and the cleaning due to it. This would allow
In prepared nursery ponds, fry of 2.5 to 4.0 cm size can
be stocked @ 1500-2000 nos/hapa of 2 x 2 x 1 m. The
most convenient cage design is a rectangular cage made
of synthetic netting attached to wooden, GI pipe or
bamboo frames. It is either a) kept afloat by styrofoam,
plastic carbuoy or b) stationary by fastening to a wooden
or bamboo pole at each corner. The size of cage varies
from 0.9 × 2.0 m and a depth of 0.9 m to 1.0 × 2.0
meters and a depth of 1.0 meter (Figure 1). The mesh
size of the nylon net is 1.0 mm. The mesh size of the
hapa should be appropriate with the size of the fishes
as well as it should allow the water movement. Water
exchange to the extent of 30% is required daily to the
pond. Fry must be fed with supplementary feed of
chopped and ground fish (4-6 mm size) @ 100% of the
water to pass through the cages more freely. Nursery
cage size may range from 3 m (3x1x1 m) to 10 m (5 x 2 x
1 m) with a mesh size of 10 mm. Cages/ hapa should be
checked and cleaned regularly. The fry on reaching a
size of 25 -40 g at the end of another rearing period of
30-45 days can be stocked in the open sea cages for
the grow-out system. Usually a survival rate ranging
from 50-70% could be obtained. The net cage should
be checked daily to ensure that it is not damaged by
crabs or clogged with fouling organisms. The cage should
be cleaned every other day by soft brushing in order to
allow water circulation in the cage.The survival rate for
the nursery period would be 50 to 80 percent. This would
depend on feeding, aquatic environmental conditions,
and the expertise of the fish farmers.
body weight, thrice a day, in the first week. The feeding
Trash fish is the main feed for seabass culture. Trash
rate is gradually reduced to 60% and 40% during second
fish should be fresh and clean. Trash fish used are
and third week respectively. The minced fish meat, made
sardines and other small marine fish. The trash fish
into small pieces of 1.5-2.5 mm, should be given as feed
should be chopped and fed thrice a day, in the early
ad libitum during the nursery rearing. Grading (removal
morning, afternoon and evening. The size must be
of shooter fish) should be done on alternative days to
suitable for the size of the mouth of the fish. The farmers
reduce cannibalism. At this stage the nets of the hapa
should give the feed slowly and watch the fish. Feeding
should be cleaned for 3 – 4 days as it gets clogged with
should be stopped when the fish no longer come up to
algal materials which reduces the water flow and the
the surface; it shows that the amount of feed is enough
water quality within the hapa. The expected survival
for them.
rate would be 80-86% with an average size of 5 to 7.5g
in 30-35 days of rearing in the hapa. However, after a
Diseases
month of nursing, they can be transferred to cages with
If hygienic conditions are maintained, the juveniles are
nylon net with mesh size of 0.5 cm. Stocking is done
generally resistant to diseases. However, since the larvae
separately for each size group. This would minimize the
are stocked in the tank for a long period, sometimes
losses from cannibalism. Fingerlings of 2.5–5.0 cms
they show their abnormal swimming character, stop
should be fed with ground trash fish at 8–10 percent of
feeding, and turn black. These are signs of disease or
body weight daily or about 4 to 5 times a day. After that,
poor health so that if these occur, they should be treated
they can be fed with finely chopped trash fish.
with 1:2,000 parts formalin solution for 10–15 minutes
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
for 2–3 days continuously. It is commonly known that
Collection, conditioning and transport of juveniles to the
the seabass fry when collected from natural areas are
grow-out systems
big enough so that they can be suitable for stocking grow
Fry are collected from the rearing tanks and placed in
out ponds and cages. As now it is able to spawn the
fiber glass tanks in the same salinity. There should be no
fish and grow the larvae and juveniles under controlled
feeding within 1–2 hours before packing. If the salinity
conditions, better knowledge is available on their growth.
of grow out is different the fishes should be acclimatized
It is also successfully completed the nursing of the
to the salinity of grow-out first before transportation. As
seabass larvae and juveniles in controlled conditions with
the fishes are now grown to a bigger size, it is better to
relatively high survival rates without much health
transport them in the bigger containers like syntax tanks
problems at present.
with aeration in good quality waters.
49
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Important management measures
in cage culture
Imelda Joseph
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
imeldajoseph@gmail.com
To get the maximum benefit out of the cultured system,
handling, loading and transport are highly stressful to fish,
given the restrictions imposed by the site, species or type
resulting not only in physical damage, but also in changes
of feed used, the stock must be kept in conditions which
in blood chemistry, increased oxygen consumption,
minimise losses and promote good growth and finally
osmoregulatory problems, and increased susceptibility to
optimum production. It is to be considered first that the
disease. Under stressful conditions, fish must expend
cages must be of a reasonable size that makes
more energy to maintain homeostasis (tendency of an
management by an individual or small group easy.
organism or cell to maintain internal equilibrium by
The major factors to be taken care in cage management
are:
z
z
z
different from terrestrial animals: they are immersed in
their environment and cannot go somewhere else. Some
appropriate to the site and rearing conditions
disease agents are almost always present in the water
Feeding the fish in the most cost effective manner
(ubiquitous). These opportunistic pathogens will invade
aimed at maximum production
fish when they become stressed. Thus, it is essential to
Ensuring the best possible water quality within the
Maintaining cages, moorings, anchors, nets and
related accessories
z
combat disease. Aquatic organisms are fundamentally
Stocking the candidate species at optimum density
cages
z
adjusting its physiological processes) and less energy to
reduce stress factors in cultured fish.
Common measures to reduce stress are:
a) Starvation before handling of fish: Handling is a source
of stress as it puts fish under extreme conditions like
Regular monitoring of the cultured species by
overcrowding. Starving the fish for 24 - 48 h (to clean
sampling, for details on health conditions, removal of
their gut of food and to reduce O2 consumption) prior
dead fishes, and treatment of infected fish
Stress reduction to the fish
to handling will reduce stress and will avoid the
deterioration of water quality when fish are
overcrowded. Seabass, Lates calcarifer, however,
Stress can be defined as any physical, chemical or
require only 1-2 h starvation prior to packing. Because
environmental stimulus which tends to disrupt normal
of rigours of journey fish should be carefully checked
well being of an animal. The processes of capture,
and injured or weak fish should be removed.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
b) Sedation during handling and transportation: In
transport fish during night or packing containers with
situations such as handling or transportation, fish are
ice and saw dust (1:1). If fish have to be transported
overcrowded. Therefore, there is a higher risk of skin
over considerable distances there is also a risk of a
injuries (scale removal, abrasion etc.). To avoid such
build up of toxic metabolites, such as CO 2 and
damages, sedation using approved fish anaesthetics/
ammonia and increased bacterial load.
sedatives is recommended as it decreases the level of
stress and possible skin injuries.
g) Lowering metabolic rate and thus oxygen
consumption and waste production : Through a
c) Grading of fish to give a homogeneous population:
combination of light sedation and hypothermia
When size variation increases in a cage, it often creates
lowering of metabolic rate and thus oxygen
competition between the larger and the smaller fish.
consumption and waste production can be achieved.
This can result in stress, especially for the smaller fish.
Absorption of ammonia and CO 2 and control of
In addition, when feeding, the bigger fish are stronger
bacterial growth through the addition of natural
and get more feed. As a consequence, the smaller fish
zeolite, a buffer and an antibiotic to the transport
get weaker and more susceptible to disease. As they
media is also practiced (only after standardization).
get sick, they will also become a source of infection
for bigger fish as size variation is also a source of
Good records of water quality conditions, growth and
cannibalism (leading to horizontal disease
mortalities should be kept so that management
transmission). For seabass, grading is essential during
procedures can be properly evaluated and modified as and
the initial stage of growth due to its cannibalistic
when necessary.
behaviour
Seed supply and stocking
d) Good water quality maintenance: Water quality should
be monitored on a regular basis and be maintained at
optimal conditions.
Any species for which seed is readily available is ideal for
cage aquaculture. Those fro which hatchery technology
is standardized is ideally suited for cage culture. Wild
e) Over-feeding to be avoided: Since over-feeding can
collected seed can also be used for cage culture if
induce stress and unconsumed feed will pollute the
adequate number is available in healthy condition. Nursery
water, it should be avoided.
rearing is very crucial for all species and specially seabass,
Transportation process: Plastic bags filled with one
f)
third with water and the remaining space filled with
oxygen prior to sealing and double bagging for safety
is better for less than 4cm fry of seabass. Insulated
(with thermocol/ saw dust etc.) transport box (1t to
with frequent grading and adequate feeding. For seabass,
if grading is not done periodically, cannibalism will
considerably reduce the stock volume. However, a 30
percent loss in stock is anticipated in normal case during
nursery rearing of fry to cage stocking size (20-30 g).
3t) mounted on truck can also be used for fish
Before stocking the fish to cages, care should be taken to
transportation. The tanks should have smooth (round)
ensure that the temperature of the fish is adjusted to
corners to minimize damage to the fish, and are often
approximately that of their new environment. It is better
provided with aeration facility during transport.
if transfer is done during evening or early morning hours.
Transport problems may be aggravated by high
When transported using tanks, the volume of water is
temperatures and by salinity. Therefore, it is better to
reduced prior to the fish being transferred by hand or net.
51
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
If nets are used, these should be of fine knotless mesh to
z
High wastage, which affects water quality
minimize damage. Feeding of fish on transfer to the cage
z
Increased bacterial load in raw diet which may lead to
can commence 3-4 h after transfer.
bacterial infection.
Feed management
Dry diet are less polluting, stable in water, nutritionally
Feed and the feeding regimes need proper management
complete, easy to transport and store, available in floating
for better health and growth of the cultured stock.
and sinking forms, etc. however, they are expensive and
However, the quality and safety of feed and the use of
formulation not known and cost escalates from one
fish medicines and chemicals must be controlled by
operation to the next depending on demand.
concerned agencies so that it will integrate aquatic
product security examination, environmental monitoring
and fish disease prophylactic systems at different levels.
Feeds and feeding
Storage of feeds
Storage facilities are essential for cage fish farming
operations. Feed bags should be stored without open
access to moisture and thus to prevent fungal attack.
Feeding is essential in cage farming especially if stocking
Trash fish may arrive at the farm in either frozen or
rate is towards the higher side or to the maximum carrying
unfrozen state and since fish spoils rapidly it should be
capacity. As in other aquaculture operations, the feeding
checked for freshness before being stored. Smell and
cost accounts for an estimated 40-60% in cage farms
appearance should be sufficient indicators of quality. Cold
also. Formulated feed meeting with the complete
storage is ideal for trash fish.
nutritional requirement of carnivorous fish is used in many
parts of the world for such species. However, the cost is
high for such feeds. Fresh or frozen minced and chopped
trash fish still forms the main stay feed for a number of
Shelf life of various feeds
Feed type
Storage and duration
Dry feeds (Rice bran,
wheat middling)
With < 10% moisture content and
stored in cool , dry and pest free
environment; can be stored for
several months
Trash fish frozen
feed with high fat content up to
three months at – 20°C; low fat
content more than one year
a t– 20°C
Pellet feeds
2-3 months
carnivore groups cultured. Economic factors and problems
with diet formulation, feed storage and distribution are
the principle reasons why this type of feed remains popular
in some quarters.
The advantages of using trash fish are:
z
Cost effective
z
Availability (of the 3mt in India @ 40 % is trash and
Feeding
used in chicken and swine feed. Why not fish feed to
Feeding should be done throughout the culture period at
fish rather than to poultry and livestock?)
varying levels depending on the growth rate and natural
feed availability. Hand feeding is done in most cases and is
The problems in using trash fish are:
z
Seasonal Fluctuation in flesh quality
z
High moisture content and expensive to transport
recommended for small scale farmers. However, mechanical
feeders are used in large scale cage farms – demand feeders
and automatic feeders are the two types of feeders used.
(best for farming operations sited close to fish landing
Feeding rings can be used if floating pellets are used. Feed
or processing centres).
trays set inside the cage at different positions can also
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
be used for feed distribution. By hand feeding, the feeding
of fish can be watched and can be fed till satisfaction.
While doing so, the stocks health status can also be
monitored (stressed or sick fish stops feeding first). Frozen
trash fish is thawed first, chopped and minced and
broadcasted over the surface using a shovel or scoop.
Water quality management
pH, ammonia and turbidity
The desirable range of early morning pH for fish production
is from 6.5 to 9. Both ammonia and nitrite are toxic to
fish. The level of ammonia toxicity depends on the species
of fish, water temperature, and pH. A healthy
phytoplankton bloom (green water) is one with a Secchi
disc visibility of 15 to 24 inches and clarity above 24 inches
indicates poor phytoplankton productivity. Visibility of less
Water quality management is a key ingredient in a
than 12 inches indicates a plankton bloom which is too
successful fish culture practice. Most periods of poor
dense and may cause low dissolved oxygen problems.
growth, disease and parasite outbreaks, and fish kills can
Visibility of less than 6 inches is critical for fish.
be traced to water quality problems. Water quality
management is undoubtedly one of the most difficult
Routine Management
problems facing the fish farmer. Water quality problems
Water quality monitoring
are even more difficult to predict and to manage
Oxygen
Monitoring of water quality is essential
z
To avoid losses caused by lethal changes in water
quality
In cage culture situations, if proper water exchange is not
there, low dissolved oxygen is particularly acute because
z
To evaluate site and configuration of cage
the fish are crowded into such small areas. Most fish kills,
z
To maintain optimum stocking and feeding
requirements
disease outbreaks, and poor growth in cage situations are
directly or indirectly due to low dissolved oxygen. Dissolved
z
oxygen management is one of the most critical
management techniques that must be learned by a fish
farmer. The cage net mesh should be kept open always to
have maximum flow of water and no drifting objects or
plants should obstruct water flow in the cage system.
To evaluate the general condition of stock, so that if
stressed, can avoid handling.
z
To gain information of long term changes in water
quality at a site so that variation in production may
be properly evaluated.
Data on dissolved oxygen and temperature are essentially
Temperature
collected. Measurements to be taken preferably at early
Temperature is critical in growth, reproduction and
morning hours and mid-day, and readings of both inside
sometimes survival. Each species of fish has an optimum
and outside cages and at cage surface and bottom should
temperature range for growth, as well as upper and lower
be made.
lethal temperatures. Below the optimum temperature
Data on nitrogen (ammonia, nitrite and nitrate) and
feed consumption and feed conversion decline until a
dissolved phosphorus, pH, turbidity etc. will give a clean
temperature is reached at which growth ceases and feed
idea about the cage environment.
consumption is limited to a maintenance ration. Below
this temperature is a lower lethal temperature at which
Waste control and effluent management
death occurs. Above the optimum temperature feed
Cage-farm wastes are usually in the form of uneaten feed
consumption increases while feed conversion declines
and fish faeces. Feed is usually the major input to the
53
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
cage-farm operations. Feeding should be scheduled in
surroundings (where pathogens can be found). However,
such a way to ensure that feed wastage is kept to a
it is necessary to reduce the risk of contamination by
minimum. Many operators now use extruded fish feed of
simple management practices aimed at reducing the
improved digestibility to maximize assimilation and
pathogen pressure in the environment. Such practices
minimise loss to the environment. Use of floating feed is
include proper system maintenance by removing excess
vital for cage-farm operations. Mooring cages in deep
suspended particles and uneaten food which is a potential
waters, leaving 3-5 m bottom space and where good
substrate for pathogens. Moreover, their presence reduces
current flow results in cage wastes being easily flushed
water flow and therefore the available dissolved oxygen
away, thereby avoiding organic build up under the cages.
for the fish. The frequency of net cleaning depends on
Health management practices
the severity of the fouling. The removal of dead or
moribund fish on a daily basis is an important sanitary
The objective of health management is to maintain a good
measure, as well as important for record keeping. Dead
health status, assuring optimum productivity and the
fish, especially in tropical water, decay quickly and can
avoidance of diseases. In aquaculture, the economic risk
be a critical source of horizontal disease transmission as
associated with diseases is high. It represents a potential
the remaining live fish will tend to eat the dead fish.
loss in production through mortality and morbidity, and
might decrease investor confidence. Moreover, the cost
to treat diseases when they are already well established
is high and treatments are often initiated too late and are
therefore rarely effective. Thus, aquatic animal health
management must be a global strategy that aims to
prevent diseases before they occur.
Selection of hatchery-raised fingerlings: The overall health
status of fry and fingerlings is a critical factor for a
successful production cycle. When choosing a species to
be farmed, preference should be given to species that are
already available from hatcheries. The attention given to
fish in the hatchery, and the availability of specific larval
diets required to obtain strong juveniles, will allow for a
Aspects of health management practices – to improve
constant supply of good quality fingerlings. Presently, the
fish health and survival
availability of hatchery-raised fingerlings is limited. The
Responsible transportation of live aquatic animals:
Increased trade of live aquatic animals and the
availability of hatchery-raised fingerlings should certainly
increase in the near future.
introduction of new species for farming, without proper
Record keeping and disease monitoring: Often, in small
quarantine and risk analysis in place, result in the further
scale operations, recording of farming parameters such as
spread of diseases. A scientific process should be
daily mortality, feed consumption, growth rate and water
undertaken to assist decision making regarding the risks
quality parameters is not standard. Record keeping is crucial
versus the benefits for the species intended to be
in understanding the epidemiology of diseases and can also
imported.
allow us to identify critical management points in the
Hygiene, disinfection and biosecurity : Hygiene and
biosecurity aims at preventing the introduction of any
production cycle. The collection of this historical data will
help us take early action in the case of disease outbreaks.
disease agent into the farm and should limit the spread
Proper disease diagnosis – a prerequisite for effective
of disease. Good sanitation practices in cage-farming
health management
systems are difficult to implement as there are no filters
As aquatic animal health management is about
or barrier between the cage environment and its
implementation of control measures to prevent the
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
incidence of diseases, it is a prerequisite to have a good
and feeding policies and timing of harvesting. Recording
understanding of diseases that might occur in a particular
of mortalities is essential, as a change in incidence of
fish species. Therefore, adequate attention should be given
mortalities can help warn of the onset of disease outbreak
to disease diagnosis and epidemiology studies.
and gives the farmer valuable information in the progress
of the stock and management strategies (stocking
Fish husbandry and management
Choosing the optimal fish density is important in cage
culture. Depending on the fish species and water quality
conditions (especially the oxygen saturation of the water),
there is a certain fish density that should not be exceeded.
A common mistake is to increase the stocking density to
compensate for a decrease in survival rate. This is a source
of stress for the fish that can lead to skin injuries, low
performance and a higher susceptibility to disease. In
contrast, stocking fish optimally will allow fish to grow
to their best potential and decrease the risk of disease
densities, feeding rates etc.)
Harvesting of fish is done continually or in batches,
depending on how the production cycle is managed.
Before harvesting the fish may be starved for a day to
have empty gut, which will help in shelf life of the produce.
Fish can be harvested in situ or the cages towed to a
convenient place where the netting operation may be
carried out more smoothly. The process of harvesting is
simple, where the net is lifted up and fishes are
concentrated to a small volume and scooped out.
outbreaks.
Maintenance of cages and gear
Regular monitoring of fish from disease point of view is
Irrespective of the damage that can be caused by storms,
also essential. Often the first signs that something is
predators, drifting objects, poachers, all materials used
wrong can be surmised from changes in behaviour. Farmers
in construction of cages have a definitive life span and
should therefore be used to observing their fish without
will eventually wear out. Cages, nets and moorings
unduly disturbing them, and form a general picture of how
therefore must be checked at intervals for signs of damage
they are disturbed and behave under normal cycle of
and wear and tear and repaired or replaced if necessary,
environmental conditions which occur at the site, i.e.,
as not only cages and stock be put at risk, through neglect,
dawn/mid day/dusk, high tide/ low tide, feeding/non-
but human life may also be endangered. Mooring must
feeding etc. changes in feeding behaviour is an indication
be checked regularly by divers, particularly after heavy
of poor health.
wind/storms. Mooring level should be kept free from
If something wrong is observed , then some fish should
fouling and worn shackles replaced.
be sampled and examined further, for changes in general
Cage nets may be checked during cleaning, which is done
physical appearance (deformed spine), skin (colour,
more frequently during cage culture. Divers may have to
presence of lesions, rashes, spots or lumps, excessive
go down and observe the net every week or so, during
mucus), eyes (bulging eyes, cloudy lens), fin and tail
favourable weather conditions. Small tears may be
(erosion) are all signs that something is wrong.
repaired at the site itself, while major repairs should be
Fish sampling should be done regularly so that the growth
done on shore only.
of stock is monitored. This information with records of
In marine environment fouling is a major issue and in
mortalities is necessary for making a number of
rotating design (single point mooring system) it is reduced.
management decisions, such as determination of stocking
Therefore, the nets have to be frequently changed. In any
55
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
case, nets of any particular mesh size should be exchanged
Net cleaning can be done physically or by chemical
quite often for ones with larger size as the fish grow. Mesh
treatment. Physical cleaning involves removing and scrubbing
size should be carefully selected at each stage of growth
the net and drying. For chemical cleaning bleaching powder
too. If too small mesh size is selected, then matter
or formic acid (3%) can be used. The rate of bio-fouling on
exchange is restricted and if too large, escape is possible.
cage frame is much slower than on net cages, and doesn’t
The frequency of net charge varies from once in a week to
need more frequent cleaning. Cage frames are usually cleaned
once in a year depending upon the site location, materials
in situ using a hand brush both above and below the water
used, season and management and design of cage.
line to dislodge weed and accumulated debris.
56
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Integration of seaweed
(Kappaphycus alvarezii) and pearl oyster
(Pinctada fucata) along with Asian seabass
(Lates calcarifer) in open sea floating cage off
Andhra Pradesh coast
Biswajit Dash, Suresh Kumar, M. and Syda Rao, G.*
Regional Centre of Central Marine Fisheries Research Institute, Visakhapatnam, Andhra Pradesh, India
*Central Marine Fisheries Research Institute, Kochi, Kerala, India
dashbiswajit999@rediffmail.com
Introduction
Aquaculture is growing very fast and its growth is
expected to continue and it is necessary to supply fish
for the ever growing population of our country. In India,
fish production and consumption is considered to be
important and needs to be promoted. As capture fisheries
have almost become stagnant, diversification of
aquaculture is highly necessary. Considering the limited
scope of freshwater aquaculture and the availability of
vast coastline, open sea cage culture gained importance
in the present day mariculture practice. Open sea floating
cage culture is an alternative sustainable practice for
rearing fish and shellfish species and polyculture along
with seaweeds may also improve profitability and
sustainability. Open sea cage culture is an aquaculture
production system where high density of fish is cultured
in floating cages. Floating cages are widely used in
commercial aquaculture and individual cage units of
the cage and to utilize this form of nitrogen and
phosphorus as the source of nutrient for the cultivation
of valuable sea weed, the study has been conducted to
see the possibility of co-cultivating sea weed
Kappaphycus alvarezii and Asian seabass Lates calcarifer
in open sea floating cage in Bay of Bengal off
Visakhapatnam coast in Andhra Pradesh. Cage culture is
an alternative sustainable practice for rearing fish and
shellfish species and polyculture along with seaweeds and
pearl producing oysters may also increase production. In
this experiment, at the open sea cage demonstration
project site at Visakhapatnam co-cultivation of Asian
seabass (Lates calcarifer), the seaweed (Kappaphycus
alvarezii) and the marine pearl producing oyster (Pinctada
fucata) was undertaken in the floating cage. It was carried
out in an offshore area near the Visakhapatnam Regional
Centre of Central Marine Fisheries Research Institute, off
Andhra Pradesh coast, Bay of Bengal, India.
desired shapes and sizes can be tailored to suit the needs.
Basics of the integrated system
The release of NO3 and PO4 from the high density of fish
Integrated cage culture with sea weed, oysters and fish
stock and due to heavy feeding from the nearby areas of
is a method of raising animals and weeds needs a floating
57
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
cage which permits a good water exchange and waste
the oysters. Proper care must be taken with regard to
removal into the surrounding water. Adequate water
floating system and buoyancy, a good service system for
circulation is essential to make the nutrients available
collars and fittings and a good mooring system and a
for the growth of the sea weed. However, the following
proper anchorage to hold the cage. A mooring system
criteria need to be given attention.
must be powerful enough to resist the worst possible
Site selection
combination of the forces of currents, wind and waves
without moving or breaking up.
Appropriate site selection is important for successful
enclosure aquaculture. Sheltered, weed-free, shallow bays
Cage positioning
(6-10 m deep) are the ideal locations for installing cages.
Positioning of the cage for good growth of fish and weed
The sites should have adequate circulation of water, with
should be done in open areas with good water circulation,
wind and wave action within moderate limits. Excessive
but protected from strong currents and high waves. It
turbulence may lead to wastage of fish energy for stabilizing
should be away from still or stagnant water where poor
themselves, loss of feed and growth of weed also may not
water quality may stress or kill fish and improper growth
be proper. The other major considerations are that the water
of the weed. It must be placed at least above 1 m above
should be pollution-free, availability of seed in the vicinity,
the bottom sediments.
easy accessibility to the site and a ready market for fish
and the weed. Flowing waters with a slow current of 1.0 to
Water quality considerations
9.0 m per minute are considered ideal for cage siting. It is
A good water area without any pollution is desired for
desirable to install cages a little away from the shore to
the culture of fish or shellfish and sea weed. Biofouling
prevent poaching and crab menace but within the limit of
caused by organisms that attach themselves to the cage
reach by the persons who monitor daily the activities.
and restrict water exchange. Area away from marine
Species selection
Selection of species for cage culture should be based on
factors like the local demands and availability of quality seed,
fast growth rate, adaptability to the stresses in enclosures
biofouling organisms include algae, oysters, clams, and
barnacles is suited or else cleaning at regular intervals
are required to facilitate a good culture activity.
Security considerations
due to crowded conditions, ready acceptance of trash fish
Cages should be placed where they can be easily
feeds and good market demand. Seaweed is opted at places
monitored if poaching is a serious consideration.
where it can be disposed off as fast as possible.
Methods applied
Cage Materials, mooring and anchoring
Experimental circular grow-out cage (15 m diameter and 6
The cage should be durable and strong, but light weight
m deep) with floating frames was used for the purpose.
and allow complete exchange of water volume every 30
Fingerlings of 80-95 mm average length which were reared
to 60 seconds by using a minimum of 13-mm square mesh
and acclimatized in 5 ton capacity FRP tanks at the
size. There should be a free passage of fish wastes and
mariculture hatchery of the regional centre were transferred
should be inexpensive and readily available. It should have
to the grow-out cage and reared at a suitable density. In
a proper net to hold the crop as well as to protect from
order to test the use of available space in the outer ring of
the predators. The outer ring should have been supported
the floating cage, thalli of the seaweed K. alvarezii were
with cat walk for daily observation of the fish, weed and
grown in nets tied with plastic rope to the HDPE outer ring
58
Central Marine Fisheries Research Institute
From 14 - 23 December 2009
of the cage. Simultaneously, epoxy coated iron boxes (2 x 2
z
Easier stock management and monitoring compared
x 0.5 ft) with plastic net covering were used to grow the
with pond culture and it shows the possibilities of
spat of P. fucata were attached to the outer ring of the
combining several types of culture within one water
cage. The spats which were bred and grown in the
body.
mariculture hatchery of the centre were used to stock in
z
the boxes with the average initial DVM 45 mm, AVM 38
Easy for daily observation of the stock allows for better
management.
mm and cup width 13 mm and an average weight of 6.22
gm. Regarding management, fish was fed only with trash
fish available at the Visakhapatnam fishing harbour at
Disadvantages:
z
Stock is vulnerable to external environmental hazards
different rates as per the biomass and no other management
like cyclones and currents and the water quality
was undertaken for the oysters and the seaweed. Sea weed
problems like algal blooms and biofouling organisms.
brought from Mandapam area of Ramanathapuram district
Rapid fouling of cage walls requires frequent cleaning
of Tamilnadu and it was grown in the mariculture hatchery
of net.
of Regional Centre of Central Marine Fisheries Research
z
Back up food store hatchery and processing are
Institute, Visakhapatnam, Andhra Pradesh. It was cut it in
necessary to overcome feeding in the fishing ban
to fragments of 30 g each and allowed to grow further, in
timings.
the 1 ton FRP tanks with 30 ppt salinity and about 30%
z
Feed losses possible through cage walls due to water
water exchange everyday. Further, it was grown in offshore
currents and sometimes the small fish enter cages
area of Lawson’s Bay at Visakhapatnam stocked in plastic
and compete for food.
net pouch of 0.5x05 ft. and the growth was recorded and
compared with onshore culture conditions. After sufficient
amount has been harvested it was re stocked in plastic net
pouch of 2.0x2.0 ft. the outer floating frame of the open
sea floating cage in square plastic rope nets of (2x2 ft) size
in which 150 gms. of sea weed were stocked. Growth of
oysters, seaweed and fish yield reached remarkable
production rates with the increment in case of fish about
212.5 %, in case of oysters with 28.8 % in DVM, 23.68 % in
AVM, 61.53 % in cup width and 296.62 % in weight and in
case of seaweed the increment was 456.66 %.
Advantages and disadvantage
Advantages:
z
z
z
Security management is must to avoid poaching as
the high density of crop is in confinement.
Conclusion
With the results presented, it can be concluded that in
open sea floating cages, the cultivation of fish, sea weed
and oysters either pearl producing or edible, provides a
reasonable solution to cultivate species that are
economically valuable and increase profitability without
much investment. In the present study, the conditions of
oysters and the seaweed were very healthy and no
negative interferences could be observed in co-culturing
fish, oyster and seaweed in the same cage indicating the
treatments and harvests remaining independent. Further
Use of existing coastal water bodies with possibility
improvement with regard to designing of the system can
of making maximum use with greatest economy with
be done when battery of open sea floating fish cages are
lower capital cost investment as compared to land-
tagged to each other with sea weeds and oysters attached
based farms.
to the outer floating frames. It provides scope for further
With its technical simplicity open sea floating cage
research to incorporate with species that could grow well
farms can be established or expanded which further
and also act as an efficient biofilter for this integrated
helps to reduce the pressures on land resources.
system.
59
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Nutritional requirements of Asian seabass,
Lates calcarifer
Ambasankar, K., Ahamad Ali, S. and Syamadayal, J.
Central Institute of Brackishwater Aquaculture
No. 75, Santhome High Road, R.A. Puram, Chennai-600 028, Tamil Nadu
ambasankar@ciba.res.in
Introduction
Asian seabass (Lates calcarifer ) has emerged as an
important candidate finfish species for aquaculture in
many parts of the world. Availability of seed and
appropriate feed are the two important prerequisites for
development and propagation of aquaculture of any fish
species. After considerable efforts and extensive research,
the Central Institute of Brackishwater Aquaculture (CIBA)
has succeeded in developing captive brood stock and seed
production technology for Asian seabass. Research efforts
on nutritional requirements and development of suitable
formulated feeds have been in progress simultaneously
at CIBA. The nutritional requirements of fish vary with
different growth stages and depend upon the feeding
habits that change according to the morphology of
digesting system. Considerable effort has been made in
nutrient requirement in the diet. Recently information
on micro-nutrient needs such as vitamins has started
coming in. The nutrition research undertaken falls clearly
into two streams viz., requirements during hatchery and
nursery phase and requirement in grow out period.
Requirements during hatchery and nursery phase
The nutritional requirements of larvae that have a body
mass less than few milligrams are not very much
understood. Based on the composition of the yolk, live
prey and larvae themselves it is assumed that the
nutritional requirements of larvae were higher than those
of the juveniles. The nutritional requirement is not similar
for larvae and juveniles. Indeed, a dietary formulation
sustaining good growth in juveniles induces poor results
in larval growth and survival.
Australia, Thailand, Philippines and more recently Israel,
Most of the works conducted on nutritional requirements
in defining the nutritional requirements of this species in
in fish have focused on lipid requirements. Until a few
order to improve production. Understanding the
years ago as there was no compound diets available for
nutritional requirements of the candidate species is the
larvae, studies on nutritional requirements are limited in
first and essential pre requisite for development of cost
general. However, studies on lipid requirements were
effective, efficient and eco friendly feeds.
easier to conduct because total lipid content or fatty acid
profile can be modified in live prey, while it is quite
Nutritional requirements
impossible to change the amino acid profile of an
Investigations on Asian seabass (also known as Bhetki in
organism. Nevertheless, growth is essentially protein
Bengal, Koduva in Tamil, Kalanchi/ Narimeen in
deposition, and adequate proteins must be supplied to
Malayalam) have been mainly concentrated on energy
sustain optimal growth.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Lipid requirements
Lipid sources and total lipid
which are found in large amount in fish cell membranes.
Experiments conducted using live prey (Watanabe and
Kiron, 1994) or a compound diet (Zambonino Infante and
Eggs of marine fish exhibit high lipid content around 20%
Cahu, 1999) have shown that the optimal level of
and reported that fertilized eggs of seabass contain about
EPA+DHA in diet for marine fish larvae is around 3% of
27% lipid on DM basis (Syamadayal et al., 2003). Lipids
dry matter.
included in microparticulate diets come partly from fish
meal or other meals incorporated as protein source and
are generally derived from marine sources. Cod liver oil,
Protein requirements
Protein sources
roe oil, sardine oil or menhaden oil are added as
triglycerides in larval diets. In seabass larvae, growth and
Person Le Ruyet et al. (1989) weaned 23-day-old seabass,
survival were directly related to the lipid content of the
Dicentrarchus labrax, with a compound diet including
diet. Best results were obtained with the diet containing
squid, shrimp and hen eggs. A mixture of fish meal, shrimp
30% lipid, as a mixture of cod liver oil and soy bean lecithin
meal, squid meal, lactic yeast was used in a diet given to
(Zambonino Infante and Cahu, 1999).
25-day-old seabass larvae (Zambonino Infante and Cahu,
1994). Protein sources were selected following their
Phospholipid
amino acid profile and incorporated in microdiet as the
Beneficial effects of phospholipid (PL) incorporation in
only protein source. Fish meal has been used as the main
larval diet was reported as early as in 1981 (Kanazawa et
protein source in diet formulated for seabass (Zambonino
al.1981) and in 1993, he has reported that fish larvae were
Infante et al., 1997) up to a level of 65% in the diet used
incapable of synthesizing PL at a sufficient rate to meet
for feeding 20 day post hatch (dph) larvae. The first
the requirement during a period of high cell multiplication;
attempt to determine optimal dietary protein level for
hence PL is required in larval diets. Studies have been
seabass at very young stages was conducted by feeding
conducted at CIBA to determine optimal level of
larvae from Day 15 to Day 35 with isoenergetic compound
phospholipids in seabass larvae using soybean lecithin as
diets incorporating a gradient in protein level (fish meal
phospholipid source. Good growth and survival have been
plus casein hydrolysate @ 30-60%). The best growth was
obtained by feeding seabass larvae with a diet containing
obtained with 50% protein.
fish oil and lecithin at 5 and 10% respectively. Sargent et
al. (1999) are of the opinion that the ideal diet for marine
Amino acid requirements
fish larvae would include 10% marine fish phospholipid,
No information is available on the amino acids
since egg or yolk sac larvae exhibit 10% phospholipid
requirement for marine fish larvae and their optimal level
concentration.
in a diet. However, the profiles of essential amino acids
Essential fatty acid
The n-3 highly unsaturated fatty acids (HUFA) have been
identified as essential dietary components for marine fish
of fish body tissue are generally considered as a good
indicator of their amino acid requirements.
Molecular form of the protein fraction
since a long time as marine fish cannot synthesize them.
The role of free amino acids and short peptides in diet on
Special attention was paid to eicosapentaenoic (EPA,
larval development has been investigated by several
C20:5n-3) and docosahexaenoic acid (DHA= C22:6n-3),
authors. As early as 1989, Fyhn (1989) suggested that
61
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
free amino acids constitute a substrate for energy
growth improvement when an amino acid mixture failed
production in marine fish larvae during early larval stages
to induce the same effect. Hydrolysates are beneficial to
and the larvae during young stages need an exogenous
larvae, while they do not affect, or in some cases, depress
supply of free amino acids. Watanabe and Kiron (1994)
juvenile growth. These results suggest that fish larvae have
considered that it is not clear if fish larvae have a sufficient
specific nutritional requirements which can be understood
ability to digest food protein or whether free amino acid
by the analysis of larval digestion.
must be provided by diet. In the same way, the
incorporation of 10% essential amino acid mixture in fish
Nutritional factors affecting larval morphogenesis
meal based diet failed to improve growth and survival in
Protein hydrolysate enhances larval morphogenesis. The
seabass larvae compared with larvae fed diet with the
molecular form of the dietary protein supply, native
same nitrogenous level brought as whole protein (Cahu
proteins or hydrolyzed into oligopeptides (around 20amino
and Zambonino Infante, 1995). Nevertheless, the dietary
acids), has probably an indirect effect on morphogenesis.
incorporation of free amino acids induced an increase in
Dietary lipids play an essential role in larval growth and
trypsin secretion in early larvae stages suggesting that
survival. Growth and normal morphogenesis increased as
pancreatic digestion would be improved. Beside their
the dietary inclusion of phospholipids and vitamins,
nutritional function, free amino acids play a very important
particularly vitamin A.
role in first feeding by acting as chemo-attractant. Protein
hydrolysate has been since a long time considered as an
Requirements during grow - out phase
advantageous protein form for fish larvae and the product
Protein and amino acids constitute the key group of
was incorporated in most of the larval diets at least for
essential nutrients required by Seabass for synthesis of
improving microparticle physical properties. Recent
protein and subsequently growth. Several studies have
experiments have shown evidence of the high nutritional
been undertaken to define protein requirements, although
value of protein hydrolysate and its role in larval nutrition.
limited studies have been undertaken to examine specific
Zambonino Infante et al. (1997) showed that a 20%
requirements for key amino acids.
replacement of fish meal by di and tripeptides (obtained
from fish meal hydrolysate) in diet resulted in
Protein
improvement of the main biological parameters in seabass
Most of the studies undertaken to examine the
larval rearing: growth, survival and skeletal formation.
requirements for protein in barramundi diets suggest a
Incorporating di- and tri-peptides to the diet led to a
relatively high protein requirement, consistent with the
Table 1. Summary of protein requirement estimates for barramundi
Crude Protein levels
examined (% to %)
35 - 55
45 - 55
45 - 55
n/d
35 - 50
29 - 55
38 - 52
44 - 65
Optimal Level
(%)
(MJ/kg)
45 - 55
50
45
40-45
50
46 - 55
52
60
Gross Energy
level at Optima
Initial Fish
Size (g)
Temp (C)
13.4 – 16.4
n/d
n/d
n/d
50
18.4 – 18.7
17.8 – 21.0
20.9 – 22.8
n/d
7.5
n/d
n/d
1.3
76
230
80
n/d
n/d
n/d
n/d
29
28
28
28
Authors
Cuzon, 1988
Sakaras et al. 1988
Sakaras et al. 1989
Wong and Chou, 1989
Catacutan and Coloso, 1995
Williams and Barlow, 1999
Williams et al. 2003
Williams et al. 2003
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Central Marine Fisheries Research Institute
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carnivorous/ piscivorous nature of the fish. Seabass being
crystalline amino acids into a lower protein diet. Both
highly carnivorous showed a dietary requirement of 45 –
studies showed that the utilisation of the crystalline
55% protein. Subsequently Catacutan and Coloso (1995)
amino acids was as effective as that of protein-bound
suggested 42.5% in the diet of the fish. Experiments
amino acids, but only at the low inclusion levels in the
conducted in CIBA with different level protein feeds on
high-protein diet. Estimations of essential amino acid
the young-ones of seabass showed a protein requirement
requirements have also been made based on the
of 43 % for this fish. The summary of protein requirement
composition of the body tissues relative ratios of key
as reported in the literature is given in Table-1.The protein
amino acids to lysine, usually regarded as the first limiting
quality in the feed influences the requirement.
amino acid in most formulated diets.
The diet energy density and the size of fish used, appear
Lipid
to be the key factors influencing the specific amount of
protein required for seabass.
Amino acids
Most of the finfish including seabass show the
requirement of the same ten amino acids (arginine,
histidine, isoleucine, leucine, lysine, methionin,
phenylalanine, threonine tryptophan, tyrosine or valine)
as essential. However, determination of quantitative
essential amino acid requirement would help in assessing
the protein requirement more accurately. There have been
several estimates of some specific amino acid
requirements for barramundi. Coloso et al. (1993)
estimated the requirement for tryptophan to be about
0.5% of dietary protein. The requirements for methionine,
lysine and arginine have also been determined to be about
2.2%, 4.9% and 3.8% of dietary protein respectively
(Millamena et al. 1994). It has been reported that
excessive dietary tyrosine can cause kidney malfunction
in barramundi (Boonyaratpalin, 1997).
Lipids comprise an important dietary energy source for
seabass and are also a source of essential fatty acids. Much
work has been devoted to exploring the inclusion of lipids
in barramundi diets to increase their energy density. At
protein levels of 45% to 50% Sakaras et al. (1988; 1989)
observed best growth from barramundi fed diets with 15%
to 18% lipid content. Studies also showed a similar growth
from barramundi fed diets with either 9% or 13% lipids,
but noted that feed conversion ratio was significantly lower
with the higher lipid levels. Studies by Catacutan and
Coloso (1995) examined inclusion levels of 5%, 10% and
15% lipids with three protein levels (35%, 42.5% and 50%).
Growth rate was highest at the 15% lipid level, provided
protein was also at the highest levels (50%). Similar growth
was also observed of fish fed diets with 10% lipids and
42.5% protein. Somatic deposition of fat was observed to
increase with dietary fat levels. In a study of some extruded
commercial diets, Glencross et al. (2003) found that two
diets of similar protein levels, but differing substantially
in lipid levels (16% vs. 22%) sustained equivalent growth
A series of experiments by Australian researchers
of 555 g fish, but that the higher lipid levels resulted in a
examined the capacity of barramundi to utilise crystalline
significantly lower feed conversion ratio. These authors
and protein-bound amino acids. One study, based on the
suggested that this was primarily a response by the fish
addition of crystalline lysine to a wheat gluten based,
to the energy density of the diets.
high-protein diet, compared its utilisation to
complementary diets modified to have an equivalent level
Essential fatty acids
of lysine enrichment, but with protein-bound amino acids.
Long-chain polyunsaturated fatty acids have been shown
A second study examined the similar addition of
to provide some essential fatty acid (EFA) value to
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
barramundi (Boonyaratpalin, 1997). Boonyaratpalin (1997),
carbohydrates. It can derive dietary energy from some
suggested that n-3 EFA levels (primarily as a mix of 20:5n-
carbohydrate sources. Research findings infer that
3 and 22:6n-3) of 1.0% to 1.7% of the diet were adequate
carbohydrate as gelatinised bread flour had some capacity
to support growth. Catacutan and Coloso (1995)
to provide dietary energy to barramundi. Fish fed diets that
examined the total lipid levels and observed signs of EFA
were iso-lipidic and iso-proteic with 20% carbohydrate
deficiency (fin erosion) at 5% dietary lipid levels.
performed better than those with only 15% carbohydrates.
Growth was significantly affected by the replacement of
Vitamins
fish oil with either canola or linseed oils, but not with
The quantitative requirements of vitamins and their
soybean oil. This observation may be due to the altered
deficiency signs in the fish are presented in Table. 2
Table 2. Summary of vitamin requirements (mg/kg of diet) for barramundi
Vitamin
Requirement (mg/kg diet)
Deficiency Signs
Thiamine
R
Poor growth, High mortality, Stress susceptible
Riboflavin
R
Erratic swimming, Cataracts
Pyridoxine
5 – 10
Erratic swimming, High mortality, Convulsions
Pantothenic acid
15 – 90
High mortality
Nicotinic acid
n/a
Fin hemorrhaging and erosion, Clubbed gills, High mortality
Biotin
n/a
Inositol
R
Choline
n/a
Folic acid
n/a
Ascorbic acid
(Vitamin C)
25 – 30a (700b)
Vitamin A
n/a
Vitamin D
n/a
Vitamin E
R
Vitamin K
n/a
Poor growth, Abnormal bone formation
Gill hemorrhages, Exophthalmia, Scoliosis, Lordosis, Broken back syndrome,
Fatty liver, Muscle degeneration, Poor gill development, Bone deformations
Muscular atrophy, Increased disease susceptibility
n-3 to n-6 ratios. Soybean oil is about 60% linoleic acid
(18:2n-6) and therefore would have substantially altered
the ratios of the diets more so than either canola or linseed
oils, both of which have substantially higher levels of n-3
fatty acids than soybean oil. An optimal n-3 to n-6 fatty
acid ratio of 1.5-1.8:1 reported for seabass with an increase
in demand at higher water temperatures. A “shock-like”
or “fainting” response was observed in some barramundi
Summary of nutrient requirements for seabass:
Nutrient
Protein
Lipid
Fatty acids
Requirement in diet
45 – 55%
6 - 18%
1.72%
(n-3 HUFA essential)
Carbohydrate
Protein : Energy ratio
Vitamin C
10 – 20%
128mg protein/kcal
700 mg/kg
from treatments where there were low levels of n-3 EFA.
References
Carbohydrates
Asian Seabass have no specific requirement for dietary
Boonyaratpalin, M. 1997. Nutrient requirements of marine food
fish cultured in Southeast Asia. Aquaculture 151, 283-313.
64
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From 14 - 23 December 2009
Cahu, C. L., Zambonino Infante, J. L. & Barbosa, V. (2003). Effect
of dietary phospholipid level and phospholipid:neutral lipid
value on the development of seabass (Dicentrarchus labrax)
larvae fed a compound diet. Br. J. Nutr. 90, 21-8.
Sakaras, W., Boonyaratpalin, M., Unpraser, N., Kumpang, P. 1989.
Optimum dietary protein energy ratio in seabass feed II.
Technical Paper No. 8. Rayong Brackishwater Fisheries Station,
Thailand, 22 pp.
Cahu, C.L. and Zambonino Infante, J.L. 1995. Maturation of the
pancreatic and intestinal digestive functions in seabass
(Dicentrarchus labrax): effect of weaning with different protein
sources. Fish Physiol. Biochem., 14: 431-437.
Sargent, J., Bell, J.G., Bell, M.V., Henderson, R. J. and Tocher, D.R.
1993. The metabolism of phospholipids and polyunsaturated
fatty acids in fish. In: Lalhou, B. and Vitiello, P. (Eds),
Aquaculture: Fundamental and Applied Research. Coastal and
Estuarine Studies, American Geophysical Union, Washington
D.C., 43, pp 103-124.
Catacuttan,M.R. and Coloso, R.M. 1995. Effect of dietary protein
to energy ratios on growth, survival, and body composition of
juvenile Asian sea bass, Lates calcarifer. Aquaculture 131, pp.
125–133
Coloso, R.M., Murillo, D.P., Borlongan, I.G. Catacutan, M.K., 1993.
Requirement of juvenile seabass Lates calcarifer Bloch, for
tryptophan. In: Program and Abstracts of the VI International
Symposium on Fish Nutrition and Feeding,
4-7 October 1993, Hobart, Australia.
Fyhn, H.J., 1989. First feeding of marine fish larvae: are free amino
acids the source of energy? Aquaculture, 80: 111-120.
Sargent, J., Mc Evoy, L., Estevez, A., Bell, G., Bell, M., Henderson,
J. and Tocher, D. 1999. Lipid nutrition of marine fish during
early development: current status and future directions.
Aquaculture, 179: 217-229.
SyamDayal, J. Ali, S.A., Thirunavukkarasu, A.R., Kailasam, M. and
Subburaj, R.2003. Nutrient and amino acid profiles of egg and
larvae of Asian seabass,Lates calcarifer (Bloch). Fish Physiol.
Biochem. 29: 141–147
Glencross, B.D., Rutherford, N., Hawkins, W.E. 2003. Determining
waste excretion parameters from barramundi aquaculture.
Fisheries Contract Report Series No. 4. Department of
Fisheries, Perth, Western Australia. pp 48.
Wanakowat, J., Boonyaratpalin, M., Pimolindja, T, Assavaaree, M.
1989. Vitamin B6 requirement of juvenile seabass Lates
calcarifer . In: The Current Status of Fish Nutrition in
Aquaculture (M. Takeda and T. Watanabe Eds.), Tokyo
University of Fisheries, Tokyo, Japan, pp. 141-147.
Kanazawa, A., 1993. Essential phospholipid of fish and crustaceans.
In: Kaushik, S.J. and Luquet, P. (Eds), Fish Nutrition in Practice,
Edition INRA, Paris, Les Colloques n°61: 519-530.
Watanabe, T. and Kiron, V. 1994. Prospects in larval fish dietetics.
Aquaculture 124: 223-251.
Kanazawa, A., Teshima, S. Inamori, S., Iwashita, T. and Nagao, A.
1981. Effect of phospholipids on growth, survival rate and
incidence of malformation in larval ayu. Mem. Fac. Fish.,
Kagoshima Univ., 30: 301-309.
Williams, K.C., Barlow, C.G. 1999. Dietary requirement and optimal
feeding practices for barramundi (Lates calcarifer). Project 92/
63, Final Report to Fisheries R&D Corporation, Canberra,
Australia. pp 95.
Millamena. O.M. 1994. Review of SEAFDEC/AQD fish nutrition and
feed development research. In: Feeds for Small-Scale
Aquaculture, Proceedings of the National Seminar-Workshop
on Fish Nutrition and Feeds (C.B. Santiago, R.M. Coloso, O.M.
Millamena, I.G., Borlongan). SEAFDEC Aquaculture
Department, Iloilo, Philippines., pp. 52-63.
Williams, K.C., Barlow, C.G., Rodgers, L., Hockings, I., Agcopra, C.,
Ruscoe, I. 2003. Asian seabass Lates calcarifer perform well
when fed pellet diets high in protein and lipid. Aquaculture
225, 191-206.
Phromkunthong, W., Boonyaratpalin, M., Storch, V. 1997. Different
concentrations of ascorbyl-2-monophosphate-magnesium as
dietary sources of vitamin C for seabass, Lates calcarifer.
Aquaculture 151, 225-243.
Zambonino Infante, J.L. and Cahu, C.L. 1994. Influence of diet on
pepsin and some pancreatic enzymes in sea bass
(Dicentrarchus labrax) larvae. Comp. Biochem. Physiol., 109:
209-212.
Ronnestad, I., Thorsen, A. and Finn, R.N. 1999. Fish larval nutrition:
a review of recent advances in the roles of amino acids.
Aquaculture, 177: 201-216.
Zambonino Infante, J.L. and Cahu, C.L. 1999. High dietary lipid
levels enhance digestive tract maturation and improve
Dicentrarchus labrax larval development. J. Nutr., 129: 11951200.
Sakaras, W., Boonyaratpalin, M., Unpraser, N., Kumpang, P. 1988.
Optimum dietary protein energy ratio in seabass feed I.
Technical Paper No. 7. Rayong Brackishwater Fisheries Station,
Thailand, 20 pp.
Zambonino Infante, J.L., Cahu, C.L. and Péres, A. 1997. Partial
substitution of di- and tripeptides for native proteins in sea
bass diet improves Dicentrarchus labrax larval development.
J. Nutr. 127: 608-614.
65
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Feeds and feeding of seabass in hatchery,
nursery and grow out system
using formulated feeds
Ambasankar, K., Ahamad Ali, S. and Syamadayal, J.
Central Institute of Brackishwater Aquaculture
No. 75, Santhome High Road, R.A. Puram, Chennai-600 028, Tamil Nadu
ambasankar@ciba.res.in
The requirement of nutrients varies throughout the life
developing larvae do not have the full complement of
cycle of an individual. At early stages, the requirement of
digestive system developed. The larvae of seabass are no
nutrients is comparatively high which declines with age.
exception to this. Studies conducted at CIBA on the
Also the requirements depend upon the feeding habits
metabolic changes and nutrient turn-over in developing
that change accordingly to the morphology of digestive
seabass larvae revealed that the growing larvae require
system. Considerable effort has been made in Australia,
the essential amino acids leucine and lysine at higher
Thailand, Philippines and more recently Israel, in defining
levels in the larval diets (Syama Dayal et al., 2003). Being
the nutritional requirements of seabass in order to improve
carnivorous, seabass larvae are fed with zooplankton such
production (Boonyaratpalin and Williams, 2001). Feeds
as rotifers for the first two weeks post hatch (PH) and
and feeding are the critical factors that determine the
then switched over to brine shrimp (Artemia) nauplii. The
economic viability of commercial aquaculture of the
size of the rotifers plays an important role in the successful
species concerned and this topic assumes much more
rearing of the larvae. Super small size rotifers are preferred
significance in a carnivore species like seabass. Based on
for feeding seabass larvae. Since, Artemia is an expensive
the nutritional requirements we know that this fish
live-food, its replacement by prepared diets has assumed
requires a high protein high energy diet. Further, being a
significance in the hatchery and nursery rearing of fish
predatory carnivore in nature, weaning them to formulated
larvae. In this context, formulated micro particulate and
feed is the critical factor which influences the success of
microencapsulated diets have been successfully used for
grow out culture of seabass. Understanding the nutritional
feeding the growing fish larvae.
requirements of the candidate species is the first and
essential pre- requisite for the development of cost
Compounded micro diets for seabass larvae
effective, efficient and eco friendly feeds.
Physical aspects
Feeding of larvae in hatchery and nursery
Size
Larvae of finfish and shellfish are generally fed with live
Diet must be prepared as microparticles, whose size must
food organisms (phytoplankton or zooplankton or both)
be adapted to the size of the larval mouth. As an example,
in the initial phase. Investigations revealed that the
size of the microparticulated diets used for seabass larval
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experiments was 50 to 125 µm at first feeding, then 125-
matrix such as agar, carrageenan or calcium alginate or by
200 µm from Day 14 to Day 25, then 200-400 µm to
a protein such as casein or zein. Microencapsulated diets
Day 40 (Cahu and Zambonino Infante, 1994). The size of
are prepared with a cross-linking agent. Microencapsulation
commercial microparticles used in hatchery for seabass
produces regular shape and water stable microparticles, but
or sea bream weaning, used from Day 40, is generally
the microcapsules can be difficult to digest. The ability of
400 to 600 µm. Accurate size of the microparticles is
larvae to break microcapsules depends on the thickness of
essential and must be well calibrated to minimize waste.
the capsule coating.
Particularly, small microparticles (less than 50 µm
Buyoancy of the diet
diameter) cannot be easily detected by larvae, whereas
large ones are difficult to ingest and may even promote a
Dietary microparticles must be distributed in large excess.
blockage of the digestive valve (Walford et al., 1991). The
Indeed, early stage larvae have a limited movement and
composition of microparticles must be homogenous;
microparticles must be caught during their fall in the water
hence, ingredients must be incorporated as very fine meal.
column. Good results can be obtained with low density
The size of the meal particles must be much smaller than
microcapsules (400-600 g/L), sinking at about 25 cm/h
the size of the final dietary microparticle. Diet, such as
average.
fish meal, must be ground and sieved before being
Visual and chemical stimuli of the diet
included in microparticles. Concerted efforts made by
CIBA scientist lead to the development of micro diets for
Light intensity, color of microparticles and tank are essential
seabass larvae and the different micro diets used for larval
for ingestion. Some pigments, such as asthaxanthin, have
rearing are given below.
been incorporated in microparticles, more for improving the
Micro diets developed at CIBA for seabass larvae
MD-200
MD-300
MD-400
Manufacturing techniques
visibility of the particle by larvae than for their nutritional
Nutrient leaching is one of the problems in developing
value. Free amino acids, such alanine, glycine and arginine
suitable diets for fish larvae. Particles must be water-stable,
and the compound betaine, have been identified as efficient
palatable and digestible. Diets used for late weaning (after
chemical stimulator for microdiet in gilthead sea bream
Day 40) in the hatchery can be crumbled, prepared by
larvae (Kolkovski et al., 1997).
grinding and sieving pellets, but diets of smaller size must
be prepared in microbound, microcoated, or
Thus, larval feed development largely depends on:
microencapsulated form. In microbound diets, the
z
Selection of nutrient specific to the species
powdered ingredients are microbound with a water stable
z
Nutritional balance of formulation
67
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
z
Retention of nutritional components
Micro diets distribution
z
Homogeneity of particles
The major bottleneck associated with micro diets feeding
z
Particle size and distribution
are over feeding of larvae and pollution of the
z
Density of particles
z
Water solubility
initially and then fall to the bottom. The larvae are not
z
Storage stability
interested in diet that are floating or lying at the bottom
z
Packing requirements
environment. The food particles must be made available
in large number around the larvae. Small particles float
of the tank but fed on those particles that pass by their
vicinity. Feeding frequencies and feeding period has to be
Apart from providing a balanced diet, the other problem
extended as the larvae are very sensitive to starvation.
related to larval rearing is the weaning of larvae. Some of
However, they can not ingest their daily ration in two to
the larvae tend to grow faster naturally than the other in
three meals as the resting time in the digestive tract of
the stock, which have to be segregated time to time for
larvae are very short compared to juveniles. These features
higher survival ability and production. These fast growing
of larvae necessitate continuous and excess feeding. Thus,
ones are not necessarily due to nutritionally imbalanced
it is essential to use feeders in larval rearing of seabass
feed but could be due to number of other factors that the
using micro diets.
hatchery operator usually faces.
Feeds and feeding of seabass in grow-out culture
Practical feeding of micro diets in sea bass larval
rearing
Weaning
The age at which weaning is carried out varies considerably
depending on the larval size and rearing method employed.
The use of micro diets in larvae is essentially preceded by
weaning them to formulated diets. The weaning of larvae
can be carried out in following ways:
1. By having a intermediate feeding phase using frozen
or freeze dried zooplankton
2. Using simultaneous distribution of live prey and dried
feed. It can be started at an early stage.
3. Co-feeding but shortening the live prey co feeding to
one or two days. This results in better size
homogeneity
In some of the East Asian countries and also in India,
seabass is cultured in grow-out ponds using low value
fish (trash fish) and tilapias in fresh condition. Since,
procurement and storage of these feed-fish is not only
laborious but also quite expensive. Hence, formulated
feeds are essential for the propagation of large-scale
farming of seabass.
Asian seabass is cultured in Australia and Thailand using
formulated feeds (Boonyaratpalin, 1991). As in the case
of other carnivorous species, feed formulations for seabass
utilize marine fish resources (for meeting protein
requirement) and fish oils along with plant protein sources.
The animal ingredients are kept above 60% of the
formulation to get protein levels in the range of 45-52%.
Experiments conducted at Muttukadu field laboratory of
CIBA had shown that feeds with substantial fishmeal
component (30-40%) only have good acceptability for
4. Starving the larvae and then introducing the micro
seabass. Higher the proportions of fishmeal better the
diets. This method can only be practiced in larvae
acceptability. The texture and size of the feed affects
which are in good health
acceptability of the feed. If the flavour and texture of the
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From 14 - 23 December 2009
feed are not to the liking of the fish, it spits out the feed
fed into an extruder by proper arrangement of water/
soon after ingesting. The use of animal protein sources
steam injection facility. The extruder operates at high
such as fishmeal is inevitable in order to keep higher
pressure (14 98 kg/cm2) and steam (Pressure 5 7 kg/cm2)
protein levels in the feed. However, plant ingredients such
injection. Depending upon the characteristics of the feed
soybean meal and other oil seed residues may be utilized
mixture and moisture content, the pressure develops
in the feed formulations. Marine fish oils should be
before the material passes through the die. Because of
included in the feed formulations as a source of
this the temperature rises and the material is forced
polyunsaturated fatty acids (PUFA). Studies conducted
through the die and the pressure suddenly drops. The
at CIBA revealed that the amino acid, glutamic acid, is a
temperature of the material rises to 110
useful feed attractant for seabass.
short spell of time and cooks the food, gelatinizing the
Seabass feeds on moving prey; hence the physical design
of the feed plays a very important role. The fish readily
accepts soft semi-moist feeds with appropriate size to
swallow vis-à-vis the size of the fish. The lower lip of the
fish is curved slightly upward, which pose disadvantage
while biting the feed. Floating and slow sinking pellet
feeds are more suited for feeding seabass. Such feeds are
generally processed in extruders.
130oC for a
starch present in the feed mixture. This imparts good
binding and water stability to the resultant pellets.
However, the pellets expand as they come out of the die
due to sudden drop of pressure and air gaps develop inside
the pellet, which makes them float or sink very slowly.
This is an excellent process for producing floating pellets
for finfish culture. By adjusting the pressure in the barrel
and moisture in the feed, it is possible to prepare sinking
pellets by extruder. The new generation extruders are
made with twin screw barrel arrangement, which are more
versatile for feed manufacture. The size of the pellet
diameter ranges from 0.5 mm to 8.0 mm.
The characteristics of extruder pellets are
Sinking feeds for seabass
z
Reduction in pellet disintegration and loss in water.
z
Increases starch digestibility due to good cooking
z
Can be worked with higher moisture and oil (fish oil)
levels in the feed.
z
Extruder pellets float or sink slowly.
z
Making charges for extruder pellets are higher due to
high cost of extruders
At CIBA, formulated feeds developed as floating and
sinking pellets were successfully tested in grow-out ponds
Floating feeds for seabass
and the fish growth was found to be 500 g in six months.
Extruder technology
The fish should be fed at the rate of 10% of their body
The basic components in an extruder are a barrel fitted
weight to start with. After four to six weeks the feeding
with a die plate and a screw shaft conveyer, which is
rate may be reduced to 8%. As the fish grow in size the
connected to a high-speed motor. The feed mixture is
feeding rate should be gradually reduced to 5%, 3% and
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National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
finally 2%. The total biomass in the pond should be
periodically estimated by suitable means (by caste
netting) for adjusting the feed. The entire quantity of feed
in a day should not be given at one time but divided and
fed 3-4 times a day.
References
Boonyaratpalin, M. 1997. Nutrient requirements of marine food
fish cultured in Southeast Asia. Aquaculture 151, 283-313.
Boonyaratpalin, M., Williams, K.C. 2001. Asian sea bass, Lates
calcarifer. In: Nutrient Requirements and Feeding of Finfish
for Aquaculture (C.D. Webster and C.E. Lim Eds.). CABI
Publishing, Wallingford, UK. pp 40-50.
Cahu, C.L. and Zambonino Infante, J.L. 1994. Early weaning of
sea bass (Dicentrarchus labrax) larvae with a compound diet:
effect on digestive enzymes. Comp. Biochem. Physiol., 109A:
213-222.
Kolkovski, S., Koven, W. and Tandler, A. 1997. The mode of action
of Artemia in enhancing utilization of microdiet by gilthead
seabream Sparus aurata larvae. Aquaculture, 155: 193-205.
SyamDayal, J. Ali, S.A., Thirunavukkarasu, A.R., Kailasam, M.
and Subburaj. R.2003. Nutrient and amino acid profiles of
egg and larvae of Asian seabass,Lates calcarifer (Bloch). Fish
Physiol. Biochem. 29: 141–147
Walford, J., Lim, T.M. and Lam, T.J. 1991. Replacing live foods
with microencapsulated diets in the rearing of sea bass
(Lates calcarifer) larvae: do they ingest and digest proteinmembrane microcapsules? Aquaculture, 92: 225-235.
70
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From 14 - 23 December 2009
Success in hatchery development of
seabass and its potential for commercial
cage culture in India
Thirunavukkarasu, A. R., Kailasam, M. and Sundaray, J. K.
Central Institute of Brackishwater Aquaculture
No. 75, Santhome High Road, R.A. Puram, Chennai-600 028, Tamil Nadu
artarasu@hotmail.com
Introduction
Brackishwater fish farming is considered as one of the
potential areas not only as a source for fish production
but also ensures the food security, livelihood for coastal
community, business opportunity for entrepreneurs and
water bodies, which is suitable for fish farming under cages
or pens can be also explored to increase the fish
production in all maritime states of India.
Culture potential
also can earn foreign exchange. Coastal aquaculture has
Among the brackishwater finfish species, the Asian
grown tremendously in early 1990s with farming of single
seabass, Lates calcarifer is considered as one of the most
species, the tiger shrimp Penaeus monodon. However,
important candidate species suitable for farming in ponds
the shrimp farming faced severe set back due to outbreak
and cages in fresh, brackish and marine water ecosystem.
of viral diseases coupled with social and other
Asian Seabass popularly known as Bhetki in India is an
environmental issues. To overcome these issues, it is
important brackishwater finfish of the family
important to introduce some of the remedial measures in
Centropomidae. The demand for seabass both in domestic
order to revive the aquaculture industry to achieve the
market and international market is increasing every year
sustainable production and one such measure clearly
because of its white tender meat.
visible is the diversification of brackishwater aquaculture
with fish species. It is evident that crop rotation can also
Development of hatchery technology
decrease the risk of disease outbreak in the pond system.
Successful seed production in the hatchery depends upon
In the recent years, reduction in large scale practices of
the availability of healthy matured fishes. For selecting
shrimp farming can be seen in most of the countries,
potential breeders, viable broodstock under captive
which is not only due to viral disease outbreak but also
conditions has to be developed. Since seabass attains
due to other reasons such as non availability quality and
maturity after 2 years of age, one has to wait more than
disease free shrimp seed, low in market price, increasing
2 years. To save time, adult fishes could be procured from
production cost etc., Due to these factors, most of the
the commercial catches, transported carefully to the
established shrimp farms have been kept idle without any
hatchery holding facilities and maintained. Healthy
farming practice. Besides, a rich resource of inland coastal
broodstock fishes after observing as protocols can be
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National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
transferred to broodstock holding facilities like RCC tanks
administration of the hormones responsible for maturation
(preferably large tanks of 50 – 100 tonne capacity) or
and spawning. Seabass spends most of its growing phase
cages or ponds for further maintenance and development
in confined waters in the coastal and inland areas and
providing required feed, quality water and healthy diet
migrates to sea for maturation and spawning.
for maturation and spawning.
Induced spawning and selection of spawners
Water Quality Management
Spawning is a “process of release of sexual gametes”.
Broodstock fishes maintained in captive condition should
Since sexes are separate in the fish, both male and female
be provided with environmental quality prevailing in the
matured fishes have to be selected for spawning. The
sea for maturation and spawning. The desirable range of
fertilization is external.
some of the water quality parameters in a broodstock
tank are
Matured female fishes will have ova with diameter more than
450 µ. Males will ooze milt if the abdomen is gently pressed.
Temperature
- 28 – 32 C
The gonadal condition is assessed by ovarian biopsy. Brood
Salinity
- 28 – 33 ppt
fishes selected for induction of spawning should be active,
pH
- 7.0 to 8.2
0
Dissolved oxygen - more than 5 ppm
free from disease, wounds or injuries. Female fishes will be
around 4 – 7 kg and males will be 2.0 – 3.0 kg. Since seabass
spawning is found to have lunar periodicity, days of new moon
Ammonia
- less than 0.1 ppm
or full moon or one or two days prior or after these days are
Nitrite-N
- less than 0.01 ppm
preferred for inducing the spawning.
Feeding and health management
Induced spawning by hormone injection
Brood fishes can be fed with trash fishes such as Tilapia
The commonly used hormones in the finfish hatcheries
or Sardines at the rate 5% body weight daily. The unfed
for induced spawning are:
feed can be removed carefully to avoid the contamination.
Fishes have to be examined monthly basis to check the
LHRH-a
- Luteinizing Hormone Releasing Hormone
analogue (Available with SIGMA
parasitic infection if any. External parasites such as
CHEMICALS – USA – ARGENT CHEMICALS)
Caligus spp. and monogenic trematode, Diplectenum
latesi, can be effectively treated either with 100 ppm
HCG
- Human Chorionic Gonadotropins.
(Available in Pharmacy – medical shops)
formalin for one hr or 1 ppm dichlorvos for one hour.
Maturation
Seabass is a protandrous hermaphrodite fish. They are
males during early stage of its life cycle and become
females in later period. Reproductive system is very much
complicated in hermaphrodite fishes since they go through
different phases of hormone secretion which is responsible
Ovaprim
- A Glaxo Product
But in the case of seabass LHRH-a hormone is found to
be effective with assured result though other hormones
can also be used singly or in combination.
Hormone dose
for gonadal development. Maturation process can be
After selecting the gravid fishes the requirement of
induced/ accelerated either by simulating the
hormone to be injected is assessed. The dosage level has
environmental conditions prevailing in sea or through the
been standardized as LHRHa at the rate 60 – 70 µg/kg
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body weight for females and 30 – 35 µg/kg body weight
is done during new moon/full moon Seabass has high
for males. The hormone in the vial (normally 1 mg) is
fecundity. It is a protracted intermittent spawner
dissolved in distilled water of known volume (5 ml). Care
(releasing eggs batch by batch). In one spawning the fish
should be taken that hormone is thoroughly dissolved.
may release 1.0 – 3.0 million eggs. The process of
The weight of the brood fishes is assessed and the required
spawning will follow during subsequent day also. If the
hormone is taken from the vials using a syringe. The fish
condition is good, both female and male respond
is held firmly. After removing one or two scale just below
simultaneously resulting spontaneous natural spawning
the dorsal fin – above the pectoral region the syringe
and fertilization is effected.
needle is inserted into the muscular region and the
hormone is administered intramuscularly gently. Since the
spawning normally occurs in the late evening hours, when
the temperature is cool, hormone is injected normally in
the early hours of the day between 0700 – 0800 hours.
Spawning tanks
Spawning tanks size depends upon the size of the fish
selected. Normally 10 – 20 tonne capacity tanks with
provision for water inlet, drainage, overflow provision and
aeration is used.
Sex ratio
Female seabass are generally larger (more than 4 kg.) and
the males are smaller (in the size of 2.0 – 3.0 kg). To
Fertilization
Fertilization is external. In natural spawning of seabass
in good maturity condition, fertilization will be 70 – 90%.
The size of the fertilized eggs will be around 0.75 – 0.80
mm. The fertilized eggs will be floating on the surface
and will be transparent. The unfertilized eggs will be
opaque and slowly sink to bottom. Due to water
hardening sometime, even the unfertilized eggs, for short
duration will be on the sub-surface but will sink
subsequently. The fertilized eggs can be collected by any
one of the following methods.
Overflow method
ensure proper fertilization normally two males are
After spawning and fertilization, the water level in the
introduced for one female in the spawning tank.
spawning tanks can be increased and allowed to overflow
through overflow outlet. The eggs will be pushed by the
Spawning
water flow. Below the overflow pipe a trough covered
Fishes injected with LHRH-a hormone response for
with bolting cloth of mesh size 150 – 200 µm is kept.
spawning after 30 – 36 hours of injection. Prior to
The water with the egg is allowed to pass through. The
spawning gradual swelling of the abdomen will be seen
eggs are collected in the next bolting cloth washed and
indicating the ovulation process. Spawning normally
transferred to the incubation tanks.
occurs late in the evening hours 1900 – 2000 hours. At
the time of spawning the fishes will be moving very fast
Scooping/ seine net collection method
and in the water surface a milky white substance will be
Since fertilized eggs will be floating on the surface, a
seen. Prior to spawning activity the males and the female
will be moving together exhibiting courtship.
bolting net cloth of 150 – 200 µm mesh size can be used
for collecting the eggs from the surface. The cloth is
Spawning activity in seabass coincides with lunar
stretched as net and towed along the water surface. The
periodicity. During full moon or new moon days, the
collected eggs after washing are transferred to the
activity is found to be in peak. Hence, induced spawning
incubation tanks.
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tanks. Larvae are stocked initially at the rate 40 – 50
Siphoning method
The water in the spawning tank is siphoned into small
tank covering with collection net cloth through which
the water will be allowed to pass through. The eggs
collected in the net cloth are transferred periodically to
nos/litre. Depending upon the age and size, the larval
density is reduced to 20 – 25 nos/l on 10th day and later
and after 15 days, the density is maintained around 10 –
15 nos/l.
incubation tanks.
Feeding the Larvae & Live Feed production
Incubation and hatching
The following live feeds are very important for feeding
The eggs collected from the spawning tank are washed
to remove the debris that would have adhered to and
the larvae
Algae
Green unicellular algae like Chlorella sp.,
transferred to the hatching tanks for incubation and
Tetraselmis sp., Nannochlorpsis or Isochrysis sp.
hatching. The hatching incubation tanks can be 200 –
are needed for feeding the live feed zooplankton.
250 L capacity cylindro-conical tanks. Eggs are kept at
density of 100 - 200 nos/litre. Continuous aeration is
Rotifer
rotundiformis is the most preferred diet for
provided. Temperature of 27 – 280C is desirable. The eggs
will hatch out in 17 – 18 hours after fertilization
undergoing developmental stages are given in the
following Table:
Rotifer ( Brachionus plicatilis ) or B.
the fish larvae in their early stages.
Artemia
Brine shrimp, Artemia in nauplii stage are
required for feeding the larvae from 9th day.
Artemia with its natural nutrient profile
Embryonic development Stages
Duration
required for larval development of fish is used
One Cell stage
Two Cell stage
Four Cell stage
Eight Cell stage
Thirty two Cell stage
Sixty four Cell stage
128 Cell stage
Blastula stage
Gastrula stage
Neurula stage
Early embryo
Heart functional and tail movement
Hatching
30 minutes
40 minutes
45 minutes
60 minutes
2 hrs
2 hrs 30 minutes
3 hrs
5 hrs 30 minutes
6 hrs 30 minutes
8 hrs
11 hrs
15 hrs
17 – 18 hrs
in all the hatcheries. .
Whatever good the culture system may be in many cases,
Rotifer or Artemia nauplii produced in the hatchery may
not be having all the nutrients required for the larvae,
(especially the unsaturated fatty acids), the cultured
Rotifer/Artemia are enriched with nutrient rich media and
then fed to the larvae.
Water Change
Water quality in the rearing tanks is very important for
The larvae are scooped gently using scoop net and
better survival and growth of the larvae. Water provided
transferred into buckets of known volume. After taking
to the larval rearing tanks should be free from flagellates,
random sample counting depending upon the number
ciliates and other unwanted pathogenic organisms. Water
required to be kept in the rearing tanks, larvae will be
should be filtered through biological filters, pressure sand
transferred to rearing tanks.
filters. UV radiation treatment is also given, to get rid of
Larval Stocking Density
the pathogenic organisms. If chlorine treated water is
drawn, residual chlorine should be removed, since, fish
Freshly hatched healthy larvae (Hatchlings) from the
larvae are highly sensitive to chlorine and water should
incubation tanks are transferred carefully to the rearing
be used only after de chlorination.
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In the larval rearing tanks, the larvae stocked as well the
assorted size rotifer can be given as feed. Artemia nauplii
live feed supplied for the larvae will excrete nitrogenous
are given as feed along with rotifers and green water from
metabolites and other debris also will accumulate. They
9th day. By this time the larvae will be around 4 mm TL in
have to be removed carefully. The debris and bottom
size. Larvae can be feed exclusively with Artemia from
sediment are removed by siphoning using siphon tubes.
16th day to 24th day. The density of the brine shrimp nauplii
The bottom debris is slowly siphoned out along with water
in the rearing medium is maintained at the rate 2000 nos./
into a trough with filter net. To maintain water quality in
l initially and gradually increased to 6000/l as the rearing
the larval rearing tanks, 30 – 40% water change is done
days progress. The daily ration of Artemia nauplii feeding
daily. The salinity should be maintained around 30 ppt.
is adjusted after assessing the unfed Artemia in the rearing
And the desirable range of temperature is 27 – 29 C. The
tank at the time of water exchange and the larval density.
0
water level reduced (30 – 40%) in the rearing tank is
leveled up with filtered quality seawater and green water
after taking cell count of the algae in the rearing tank.
Algal water is added daily up to 15 day. After bottom
th
cleaning and water reduction, while water change is done,
algal water is also added depending upon the
concentration, (around 20 thousand cells/ ml in the
Feed density/quantity to be given to seabass
By 21st day the larvae will be around 10 – 11 mm TL in size
after completing larval development stages. From 25th
day the larvae can be fed with Artemia sub adult (biomass)
along with cooked minced fish/shrimp meat. The fry can
also he weaned slowly to artificial feed.
Algal water added should not be
Under circumstances, when the rotifers could not be fed
contaminated since in the open culture there is chance
with marine Chlorella adequately, the nutritional quality
of contamination by flagellates, ciliates and filamentous
of such rotifers may be poor. In such case, the rotifers
algae which will be toxic to the fish larvae. Apart from
can be enriched with special enrichment media.
being a source of feed for the rotifers in the tank, the
Enrichment is done by keeping the rotifers in emulsified
algae also help in the conversion of harmful excretory
enrichment medium like SELCO DHA or cod-liver oil for
products like ammonia and other metabolites in the
18 - 24 hours. By this process, the animals will ingest
rearing container into less harmful nutrients.
the enrichment media which is rich in Poly unsaturated
rearing tank
Fatty Acids (PUFA), required for larval growth. The animals
Feeding
are washed and fed to the larvae. In this way Rotifers
Rotifer (Brachionus plicatilis) is given as feed to the larvae
Artemia nauplii/ Artemia biomass can also be enriched
from 3 day. Rotifer is maintained in the larval rearing
and fed. Moina, a cladoceran can also be fed to the
tanks at concentration at the rate 5 nos./ml initially. From
seabass larvae after 21 days.
rd
4 day to 15 day the rotifer concentration is increased
th
th
to 10 – 20 nos./ml gradually. Every day after water
Grading
exchange, the food concentration in the tank should be
Seabass while growing exhibits differential growth rate,
assessed and fresh rotifers should be added to the required
hierarchy, resulting different size groups in the same
concentration. In the early stages (3 – 5 days) the larvae
rearing tank. The large one’s shooters dominate others
may not be in a position to ingest the large sized rotifers.
for food and space and also prey on them. Seabass larvae
Hence after collecting the rotifers from the tanks small
are highly cannibalistic and it is more pronounced in early
sized rotifer less than 1500 µm should be sieved using
stages. In the rearing tanks, when the larval concentration
suitable mesh size bolting cloth nets. . From 6 day
is more and congregation takes place for food and feeding,
th
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
the larger ones are tempted to feed on the smaller ones.
Artemia biomass is seen, seabass fry are stocked at the
To avoid this problem, regular grading has to be done.
rate 800 – 1000 nos/m3. The pre-adult Artemia would
The large sized larvae, (“Shooters”) have to be removed.
form good food for seabass fry. The fry would not suffer
Uniform sized larvae should be kept in the rearing tanks
for want of food in the transitional nursery phase in the
for better survival and growth. Grading should be done
tank since the larvae are habituated to feed on Artemia
th
once in three days from 15 day or whenever different
in the larval rearing phase. Along with ‘Artemia biomass’
size larvae are seen in the tanks. Grading can be done
available as feed inside the tank supplementary feed
using a series of fish graders with different pore size of 2
mainly minced fish/shrimp meat is passes through a mesh
mm, 4 mm, 6 mm, 8 mm, 10 mm. When the larvae are
net to make each particle of size of around 3 – 5 mm and
allowed to pass through the graders, different size will be
cladocerans like Moina sp can also be given. The fish/
retained according to pore size of the sieves. Grading
shrimp meat feeding has to be done daily 3 – 4 times.
may cause injuries leading to mortality. Hence proper
Feeding rate is 100% of the body weight in the first week
care should be taken in handling the larvae. Prophylactic
of rearing. This is gradually reduced to 80%, 60%, 40%
treatment with 5 ppm Acriflavin can be given. By adopting
and 20% during 2nd, 3rd, 4th and 5th week respectively.
these practices survival rate up to 48% has been achieved
Regular water change to an extent of 70% is to be done
with average survival rate of around 15 % in 25 days in
daily. The left over feed and the metabolites have to be
larval rearing phase. After rearing the larvae in the
removed daily and aeration should be provided. In a rearing
hatchery for 25 – 30 days the fry can be transferred to
period of 4-5 weeks in the nursery rearing, the seed will
nurseries for further growing.
be in the size of 1.5 to 3.0 g/ 4-6 cm with survival rate of
Nursery rearing
60-70%. Adopting this technique at a stocking density
at the rate 1000 nos/m3 in the hatchery, survival rate up
Nursery Rearing in Hatcheries
to 80% has been achieved. For the better survival during
Seabass fry of 25 – 30 days old in the size of 1.0 – 1.5 cm
early growth phase, regular Grading should be done.
can be stocked in the nursery tanks of 5 – 10 tonn capacity
Vessels/trough placed with different mesh sized nets can
circular or rectangular (RCC or FRP) tanks. Outdoor tanks
be used for grading. When the seed are left into the
are preferable. The tanks should have water inlet and
containers the seeds will be sieved in different grades
outlet provision. Flow through provision is desirable. In
according to the mesh size and seed size. Care should be
situ biological filter outside the rearing tanks would help
taken that the fry are not injured while handling. If the
in the maintenance of water quality. The water level in
number is less it could be manually done.
the rearing tanks should be 70 – 80 cms. Good aeration
facility should be provided in the nursery tanks. After
Status of seabass farming
filling with water 30 – 40 cm and fertilized with
Amongst the cultivable fishes in India, Seabass fetches
ammonium sulphate, urea and superphosphate at the rate
higher price in domestic market varying between Rs.100-
50, 5 and 5 gm (10: 1 : 1 ratio) per 10 tonne of water
250 per kg depending upon the size, the availability and
respectively. The natural algal growth would appear within
season. It is extensively cultured, in South East Asian
2-4 days. In these tanks freshly hatched Artemia nauplli
Countries like Thailand, Malaysia, Singapore and Australia.
at the rate 500 – 1000 l are stocked after leveling the
Culture of seabass is relatively easy and dependable with
water to 70 – 80 cm. The nauplii stocked are allowed to
fewer risks. Based on case studies, in Thailand it has been
grow into biomass feeding with rice bran. When sufficient
estimated that the production of seabass culture was 20.5
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From 14 - 23 December 2009
kg/m3. The price of seabass is US$2.27 per kg. The total
Aquaculturists. With the advances in the technology in
income from the cage is US $ 46.49 per m . The rearing
the production of seed under captivity assuring the supply
cost is US $ 24.15. The net return is US $ 22.34 per m .
of uniform sized seed for stocking and quality feed for
In the culture operation the fixed cost in cage culture is
feeding, the seabass culture is done in South East Asian
only 5.9%. The variable costs such as feed, seed, labour
Countries and Australia in more organized manner. The
etc cost 94.1%. The feed alone costs 63%, followed by
major problem in the development of seabass aquaculture
the seed cost. Seabass, the value added finfish can be
in India is the availability of seed in adequate quantity
considered as a complementary to shrimp for the
and the time of need and quality feed for nursery rearing
sustainability of brackishwater aquaculture.
and grow out culture. The former has been overcome
2
3
Traditional Culture
and the technology package for the seed production of
seabass under controlled conditions is available. The
Seabass is cultured in the ponds traditionally as an
suitable feed for the culture of seabass is being developed.
extensive type culture throughout the areas in the Indo-
The seed production technology developed by CIBA has
pacific region where seabass is distributed. In low lying
already been commercialized and the feed technology will
excavated ponds, whenever the seabass juveniles are
be ready shortly for commercialisation.
available in the wild seed collection centers (For eg. April
technological improvements in the seabass culture have
June in West Bengal, May-August in Andhra Pradesh,
motivated the farmers to select seabass as a candidate
Sept-Nov. in Tamil Nadu, May to July in Kerala and June-
species for aquaculture. Farmers have been adopting
July in Maharashtra. Juveniles of assorted size seabass
improved farming practices in seabass culture.
These
are collected and introduced into the traditional ponds
which will be already with some species of fish, shrimps
Improved Seabass Culture Methods
and prawns. These ponds will have the water source from
The traditional culture method is improved with stocking
adjoining brackishwater or freshwater canals, or from
of uniform sized seed at specific density and fed with low
monsoon flood. The juvenile seabass introduced in the
cost trash fishes/formulated feed of required quantity.
pond will prey upon the available fish or shrimp juveniles
Water quality is maintained with exchange periodically.
as much as available and grow. Since, seabass by nature
Fishes are allowed to grow to marketable size, harvested
is a species with differential growth are introduced into
and marketed for high unit price. Seabass culture can be
the pond at times of food scarce, the larger may resort to
done in more organized manner as a small-scale/large
feed upon the smaller ones reducing the number. Seabass
scale aquaculture in brackishwater and freshwater ponds
are allowed to grow for 6-7 months of culture period till
in cages.
such time water level is available in these ponds and then
harvested. At the time of harvesting there will be large
fish of 4 to 5 kgs as well as very small fishes. In this
manner production up to 2 ton/ha/7-8 months have been
obtained depending upon the number and size of the
fishes entered/introduced into the pond and the feed
available in the pond.
Polyculture
This is an improvement over the traditional method, where
the feed, the live fishes, shrimps are deliberately allowed
in to the seabass culture ponds to serve as facilitating
feed for the seabass in the pond. In the traditional method
there is no control over the quantity and quality of the
However, this practice is highly unorganized and without
feed entering the ponds which may or may not be
any guarantee on production or return for the
adequate. At times of scarcity for feed, the seabass may
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National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
resort to cannibalism resulting in low survival and
Floating cages: The net cages are attached to wooden
production though few fishes will be large size. Under
frames kept afloat using plastic drums. Anchors or
polyculture method, the feed in the form of forage fishes
Concrete weight blocks as anchors can be attached to
are produced in the culture ponds itself and made available
the corners of the net cage at the bottom. These types
to the seabass fish to prey upon as and when it requires.
of cages can be installed in areas with water depth more
Grow out culture of seabass in cages
Fish culture in cages has been identified as one of the
eco-friendly at the same time intensive culture practice
for increasing in fish production. Cages can be installed
in open sea or in coastal area. The former is yet to be
developed in many countries where seabass is cultured
but coastal cage culture is an established household
activity in the South East Asian countries. There are
than 4 meters with feeble water current.
Stationary cages: These are fixed enclosures, which can
be installed, in shallow water areas in lagoons,
brackishwater lakes having water depth of 2-4 meters.
The cage net is fastened to wooden poles erected in the
water system at the four corners.
Stocking Density
abundant potential as in India also for cage culture in the
In the cages, fishes can be stocked at the rate 25-30nos/
lagoons, protected coastal areas, estuaries and Creeks.
m3 initially when they are in the size of 10-15 gm. As
Since, cage culture of seabass has been proved to be a
they grow, after 2-3 months culture, when they are around
technically feasible and viable proposition this can be
100-150 g stocking density has to be reduced to 10-12
taken up in a large scale in suitable areas.
nos/m3 for space. Cage culture is normally done in two
phase – till they attain 100-150 gms size in 2-3 months
Cage culture system allows high stocking density, assures
and afterwards till they attain 600-800 in 5 months.
high survival rate. It is natural and eco-friendly and can
be adapted to any scale. Feeding can be controlled and
Feeding in Cage
cages can be easily managed. Harvesting is not expensive.
Fishes in the cage can be fed with either extruded pellets
Water depth and water current alone the criteria. Even
or with low cost fishes as per the availability and cost.
in areas, where the topography of the bottom is unsuitable
Floating pellets have advantages of procurement, storage
for pond construction, cage can be installed. Diseases
and feeding. Since, a lot of low cost fishes are landed in
can be easily monitored.
Fishes in the cages can be
the commercial landings in the coastal areas which are
harvested as per the requirement of the consumers, which
fetching around Rs.3-5/kg only used as feed for seabass
will fetch high unit price. Above all, cage culture has got
culture. Low cost fishes like Tilapia available in the
low capital input and operating costs are minimal. Cages
freshwater and brackishwater also serve as feed for
can be relocated whenever necessary to avoid any
seabass in ponds and in many cage culture operations.
unfavorable condition.
The rate of feeding can be maintained around 20% initially
Design of Cages
and reduced 10% and 5% gradually in the case of trash
Grow out cages of 20 or 50 m2 are preferable for easy
management and maintenance. Cages are fabricated with
polyethylene netting with mesh size ranging from 2 to 8
fish feeding and in the pellet feeding, the feeding rate
can be around 5% initially and gradually reduced to 2-3%
at later stage.
cm depending upon juvenile fish propose to stocked in
In the feeding of low cost fish FCR works out around 6 or
the cages. There are two types of cages:
7 (i.e. 7 kg of cheaper fishes has to be given for one kg of
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From 14 - 23 December 2009
seabass). In the case pelleted feeding FCR is claimed to
be around 1 to 1.2 in Australia. However, the cost
effectiveness of the pellet feeding for seabass in grow
out culture has to be tested.
Cage farming in India can be taken up in pilot scale by
utilizing different ecosystem. Cost effectiveness of
seabass cage farming with formulated feed in high density
in the marine water ecosystem has to be evaluated. The
Cage Management
Since cages are inside the water and exposed to water
current, the debris materials drifted may adhere to the
cages and clog the mesh restricting the water exchange.
The fouling organism will also attach and clog the meshes.
Other animals like Crab may damage the nets. The cages
should be regularly checked for clogs and leaks. Damaged
nets should be repaired or replaced.
Conclusion
The clogging will
reduce water exchange, and lead to accumulation of waste
products depleting the oxygen causing stress to the fishes,
affecting feeding and growth. If the damage is not repaired
immediately, the fishes will escape from the cages.
Production
Under cage culture, since seabass can be intensively
stocked and properly managed, the production will be
high. Frequently culling and maintenance of uniform sized
fishes in to the cages will ensure uniform growth and high
production. Production of 6-8 kg/m2 is possible in the
cages, under normal maintenance and production as high
as 20-25 kg/m2 is obtained in intensive cage management
in the culture of seabass.
Integration of cage culture of seabass with shrimp
culture
If seabass can be weaned to feed on floating pellets,
because of their addictive nature to selective feed, they
will not resort to prey upon shrimp as normally
experienced in shrimp culture ponds. If the water depth
can be maintained around 1.5-2.0 m, in a pond, cages
can be installed in the shrimp culture pond itself and
seabass seed weaned to feed on floating pellets can be
stocked in the cages and reared. In this way, seabass
culture will be a complimentary to shrimp culture.
production of value added species like seabass will be
increased by using marine and freshwater reservoir cage
system. There is need of creation of infrastructure
facilities to carry out the nursery rearing and cage farming
of the seabass. The safety and security of the stock has
to be assured since the fisheries in marine water are prone
to poaching. The value and importance of the cage farming
has to be taken as massive awareness programme in the
surrounding areas. The programme can be initiated as a
community programme through fishermen/women cooperatives.
Further Reading
A book on simplified hatchery technology for seabass, Lates
calcarifer seed production (2006). Central Institute of
Brackishwater Aquaculture, Chennai, India A.R.T.Arasu,
M.Kailsam, J.K.Sundaray, M. Abraham, R.Suburaj,
G.Thiagrajan & K.Karaiyan.
Arasu, A.R.T., M. Natarajan, M. Kailasam and J K Sundaray
(2008). Induced breeding techniques in Brackishwater Fin
Fishes. Pp7-14 in the proceedings of National Seminar on
Recent Trends in Aquaculture Biotechnology held at Jamal
Mohamed College, Tiruchirapalli, Tamil Nadu sponsored by
University Grant Commission., August 2008.
Asian Seabass fish seed Production and culture. (2009) CIBA
special publication No-42, Edited by A.R.T. Arasu, M.
Kailasam & J K Sundaray
Biswas, G., A. R. Thirunavukkarasu, J. K. Sundaray and M.
Kailasam (2008). Effect of stocking density on the growth
dispersion in Asian seabass Lates calcarifer (BLOCH) under
nursery rearing presented in the 8th Indian Fisheries Forum
held on 22nd to 26th November 2008 at CIFRI, Barrackpore,
Kolkata.
.Arasu, A.R.T, M, Kailasam, J.K.Sundaray, R.Subburaj,
G.Thiagarajan and K.Karaiyan. Improved hatchery technology
for Asian seabass Lates calcarifer (Bloch) (2008). CIBA
special publication No.34. pp 1-38
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National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Sundaray, J.K., A.R.T.Arasu, M. Kailasam and G. Biswas (2008).
Reproductive hormones in fishes in the proceedings of National
Seminar on Recent Trends in Aquaculture Biotechnology held
at Jamal Mohamed College, Tiruchirapalli, Tamil Nadu sponsored
by University Grant Commission., pp.15-21, August 2008.
Kailasam, M., Thirunavukkarasu A.R, Selvaraj,S and P.Stalin
2007. Effect of delayed initial feeding on growth and survival
of Asian seabass Lates calcarifer (Bloch). Aquaculture 271
(2007) 298-306
Kailasam, M., A.R.Thirunavukkarasu, J.K.Sundaray, Mathew
Abraham, R.Subburaj, G.Thiagarajan and K.Karaiyan 2006.
Evaluation of different feeds for nursery rearing of Asian
sea bass Lates calcarifer (Bloch) Indian Journal of Fisheries
53 (2): 185-190.
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Importance of water quality in marine life
cage culture
Prema, D.
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
premadicar@gmail.com
Water quality in marine life cage culture is one of the
most important factors that determine production and
mortality. Choice of site for marine cage culture is of
paramount importance since; it not only affects water
quality but also greatly influences the economic viability.
Once the site is selected for marine cage culture, there is
little that can be done to improve the site, if water
exchange is poor.
Criteria for selecting a site for marine cage culture
Environmental Criteria
Wind
The wind can determine the suitability of a particular site
or area for cage fish culture through its influence on cage
structures and caged stock. Of particular concerns are
violent storms. But up to certain level, effects due to
moderate winds can be profitable by the mixing of water.
Maximum permissible wind limit is 30 – 40 km hr-1. The
wind velocity limit also emphasis the need of suitable
season for marine cage culture when wind velocity is low.
The cage culture of sea bass conducted by CMFRI, Cochin
was during October – April in the open sea, at Munambam,
Depth
off Cochin. In the Arabian sea, during June – August, the
Shallow bays with limited depth of water under cages are
winds blow at their greatest strength and by September,
not favorable for water renewal and generally the settling
the wind velocity decreases and by October – November,
of wastes. A depth of 10 – 30m at low tide may be
the wind starts blowing from north westerly to north
considered as ideal condition. Cages should be sited in
easterly with comparatively low velocities.
sufficient depth to maximize the exchange of water, yet
keep the cage bottom well above the substrate in order to
Waves
avoid interaction between the cage bottom and sea floor.
Wind driven waves are propagated by the frictional drag
Water is drawn into the cage not only through the sides
of wind by the wind blowing across a stretch of water
but also through the bottom panel and as the cage bottom
that transfers energy to the fluid. Wave size is determined
approaches the substrate, flows become increasingly
by wind velocity, wind duration and the distance of open,
impeded. It can cause chemical and bacterial interactions,
unobstructed water across which the wind blows; and is
net damage and predation of the fish by crab and bottom
also influenced by the waves present when the wind starts
organisms. The cage of sea bass established by CMFRI,
to blow. At the windward end, waves are poorly developed
Cochin was at a depth of 10 m in inshore area off Cochin.
with small wave heights and short periods of oscillation.
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However, waves develop with distance, reaching
maximum size when they attain the same velocity as the
wind. Wave height increases with wind velocity and wave
energy increases proportionally with square of wave
height. The maximum limit of wave height for working on
floating cages is 1m.
Substrate
The cage site substrate range from rocky to soft mud.
Mud or rock bottom may cause difficulties for a safe and
reliable anchorage for cage. A sandy or gravel bottom is
generally looked for.
Currents and tide
Water Quality Criteria
Good water exchange through cages is essential both for
Temperature and salinity
replenishment of oxygen and removal of waste
metabolites. A weak and continuous current stream is
favorable to bring oxygen and remove wastes in a cage.
However excessive currents impose additional dynamic
loadings damaging floating structures or cages, reduce
the cage usable volume due to the deformations of the
net and may adversely affect fish behavior. The limit for
current velocity is with a minimum of 0.05 m S-1 to a
maximum of 1 m S-1.
Fish and other farmed organisms have no means of
controlling body temperature, which changes with that
of environment. A rise in temperature increases
metabolic rate and causes a concomitant increase in
oxygen consumption and activity as well as production
of ammonia and carbon dioxide. Salinity is a measure of
the amount of dissolved solids present in water and is
usually expressed in parts per thousand. Its relevance
to cage culture lies principally in its control of osmotic
In all except a few coastal regions of the world, tidal
pressure, which greatly affects the ionic balance of
currents are the predominant source of surface water
aquatic animals. Rapidly fluctuating conditions of
currents. Attractive forces exerted by the moon and sun
temperature and salinities are harmful for marine life
on the Earth produce tidal waves. The crest and trough of
cage culture. Seasonal changes are also to be taken care
the wave are termed high and low tide respectively, while
of during the culture period. For most tropical marine
the wave height is referred to as the tidal range. Associated
life aquaculture, a temperature of 26 - 28ºC in early
with the rise and fall of the tide are the horizontal motions
morning with no abrupt changes is considered as
of water or tidal currents. Maximum current velocity occur
suitable. Similarly preferred salinity range is 25 – 40 ppt,
at the middle of the rise (flood) and fall (ebb) ie., during
evading abrupt changes.
the mid time between highest and lowest tide. For marine
cage culture, limited tide amplitude (<1m) is preferred.
Dissolved Oxygen
Based on the tide table for the particular area of the coast,
Dissolved oxygen is required by all higher marine
current velocity thus can be predicted in pre-monsoon
organisms for the production of energy for essential
and post-monsoon season during a cage culture period.
functions such as digestion and assimilation of food,
But in monsoon, current velocity is unpredictable. Current
maintenance of osmotic balance and activity. Oxygen
velocity during monsoon is mainly influenced by littoral
requirements vary with species, stage of development,
current, strong winds, wave effects and increased river
size and are also influenced by environmental factors such
discharge. Hence there is every chance that current
as temperature. If the supply of oxygen deviates from the
velocity can exceed its permissible maximum limit
ideal feeding, food conversion, growth and health can be
prescribed for marine cage culture. Monsoon season is
adversely affected. It is therefore important that good
generally avoided for marine cage culture activity.
oxygen conditions prevail at a site.
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During the day, there is a net production of oxygen, but at
ranging in size from colloidal to coarse dispersions. Turbid
night, when photosynthesis stops, the algal community in
conditions arise from organic or inorganic solids suspended
water becomes a net oxygen consumer. Where there are
in the water column as a result of soil erosion, mining
large algal communities, super saturation of DO may occur
wastes and other industrial effluents. Cage fish farms are
during the day and sub saturation condition prevail at night,
themselves a source of suspended solids.
with late afternoon maxima and pre-dawn minima,
stressing fish. The environmental conditions conducive to
blooms usually occur during the warmer months in areas
subject to high nutrient influxes. External sources such as
sewage discharges and agricultural run off may be important
contributors. However, a sudden upwelling of nutrient rich
water from deeper layers of the water body during the break
down of stratification may also stimulate blooms. Problems
can occur when algal blooms die. During decomposition,
microbial respiration may remove much or even the entire
DO resulting in fish kills.
Benthic oxygen demand can cause de-oxygenation of the
hypolimnion. Good mixing, water exchange and flushing
by proper currents, tides and winds is a must in order to
shun this situation. Marine sites which have good bottom
current which disperse settling wastes are desirable.
Preferred DO level for marine life culture is >6 mg l-1.
The quantity and quality of material suspended in water
column at any particular moment is largely determined
by water movement, which transports, fractionates and
modifies solids. Large, dense particles are more easily
settled than small, less dense particles. Water currents
can also prevent particles from settling and re-suspend
settled materials. Water chemistry and salinity in
particular influences turbidity through its effect on
flocculation and settling and is important in the transport
of sediments.
High levels of suspended solids cause gill damage,
inducing the gill epithelial tissues to proliferate and
thicken. If damage is sufficiently severe, the fish will die.
Turbidity levels less than 100 mg l-1 have little effect on
most species. However, duration of exposure is important.
Preferred range of dry suspended matter for marine life
cage culture is <2 mg l-1.
pH
pH is a measure of hydrogen ion concentration of a
Color / Transparency
solution. pH is important to aquatic life because extreme
Part of the light (solar radiation) striking water does not
values of it can damage gill surfaces, leading to death
penetrate the surface. A portion is reflected depending
and because it affects the toxicity of several common
on the roughness of the water surface and the angle of
pollutants like ammonia and heavy metals.
radiation. As light passes through water, scattering and
differential absorption by the water takes place. Turbidity
The pH of sea water usually lies in the range 7.5 – 8.5. Sea
and color in water may result from colloidal clay particles,
water is also well buffered ie., comparatively resistant to
from colloidal or dissolved organic matter or from an
changes in pH through the addition of alkaline or acidic
abundance of plankton. Secchi disk visibility can be taken
compounds. Preferred pH for marine life culture is 7.8 – 8.4.
as a measure of colour / transparency of the water in
Turbidity
marine life cage culture. The Secchi disk is a weighted
Total suspended solids
disk, 20 cm in diameter and painted in alternate black
and white quadrants. The average of depths at which the
Turbidity refers to the decreased ability of water to
disk disappears and reappears is the Secchi disk visibility.
transmit light caused by suspended particulate matter
Optimum transparency expressed as Secchi disk visibility
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for marine culture is <5 m as yearly mean. Transparency
growth. Preferred range of Ammonia N as (NH4 + NH3)
is an important factor deciding light penetration and
for marine culture is < 0.1 mg l-1.
euphotic zone (the stratum of water receiving 1% or more
of incident radiation, where, photosynthesis proceeds at
Nitrite N
rates exceeding respiration), affecting the primary
Nitrite originates as an intermediary product of
productivity and oxygenation of the culture water.
nitrification of ammoniacal N by aerobic bacteria. Marine
water has high concentration of calcium and chloride
Total inorganic nitrogen
Ammonia N
Ammonia is the most toxic form of inorganic N produced
in water. The major source of ammonia in water is the
direct excretion of ammonia by fish. It also originates from
the mineralization of organic matter by heterotrophic
which tend to reduce nitrite toxicity.
Nitrate N
Nitrate is the end product of nitrification of ammoniacal
nitrogen by aerobic autotrophs. Its presence can also be
due to land drainage.
bacteria and as a by product of nitrogen metabolism by
The total inorganic nitrogen for marine life culture is <
most aquatic animals. Both ammonia (NH 3 ) and
0.1 mg l-1.
ammonium (NH4+) are toxic, but NH3 is much more toxic
than NH4+. Ammonia toxicity increases with the increase
Total inorganic phosphorus
in pH and temperature.
Phosphorus (P) is found in the form of inorganic and
The ammoniacal N content of water is an index of the
organic phosphates (PO4) in natural waters. Inorganic
degree of pllution. Its concentration in unpolluted water
should never be more than 0.1 mg l-1 and below this level,
healthy growth of fish is expected. Aquatic autotrophs
rapidly utilize ammonium ions, thus naturally preventing
it from reducing to toxic levels.
As ammonia concentration increases in water, ammonia
excretion by fish decreases and levels of ammonia in blood
and other tissues increase. This results in an elevation of
phosphates include orthophosphate and polyphosphate
while organic forms are those organically-bound
phosphates. Phosphorous is a limiting nutrient needed
for the growth of all plants - aquatic plants and algae
alike. However, excess concentrations of P can result to
algal blooms. The total inorganic phosphorus for marine
life culture is < 0.015 mg l-1.
COD (Chemical Oxygen Demand)
blood pH and adverse effects on enzyme catalyzed
The COD of water represents the amount of oxygen
reactions and membrane stability. High ammonia
required to oxidize all the organic matter, both
concentrations in water also affect the permeability of
biodegradable and non biodegradable by a strong chemical
fish by water and reduce internal ion concentrations.
oxidant. Preferred Chemical Oxygen Demand for marine
Ammonia also increases oxygen consumption by tissues,
life culture is < 1 mg l-1.
damages gills and reduces the ability of blood to transport
oxygen. Histological changes occur in kidneys, spleen,
Chlorine
thyroid and blood of fish exposed to sub-lethal
Both free and combined, residual available chlorine are
concentrations of ammonia. Chronic exposure to
extremely toxic to fish. The measurable concentrations of
ammonia increases susceptibility to diseases and reduces
chlorine in water for marine life culture is <0.02 mg l-1.
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Heavy metals
anthropogenic sources. Anthropogenic sources of copper
They originate mainly from anthropogenic industrial
pollution. The toxicity of heavy metals is related to the
dissolved ionic form of the metal rather than total
concentration of the metal.
in the environment include corrosion of brass and copper
pipes by acidic waters, industrial effluents and fallout,
sewage effluents, and the use of copper compounds such
as copper sulphate as aquatic algicides. Major industrial
sources of copper include smelting and refining industries,
copper wire mills, electroplating, metal finishing, coal
Mercury
Mercury (Hg) is toxic to both aquatic life and humans.
Inorganic form occurs naturally in rocks and soils. It is
being transported to the surface water through erosion
and weathering. However, higher concentrations can be
burning, and iron and steel producing industries. Large
quantities of copper can enter surface waters, particularly
acidic mine drainage waters, as a result of metallurgical
processes and mining operations.
found in areas near the industries. The most common
The toxicity of copper to marine organisms in marine and
sources are caustic soda, fossil fuel combustion, paint,
estuarine environments is influenced by physical factors
pulp and paper, batteries, dental amalgam and
and chemical characteristics of the marine environment:
bactericides.
The copper in water for marine life culture should be <0.02
Mercury remains in its inorganic form (which is less toxic)
until the environment becomes favorable, i.e. low pH, low
dissolved oxygen, and high organic matter where some
mg l-1.
Pesticides
of them are converted into methylmercury (the more toxic
Pesticide refers to any chemical used to control unwanted
organic form). Methylmercury tends to accumulate in the
non-pathogenic organisms, including insecticides,
fish tissue, thus making the fishes unsafe to eat.
acaricides, herbicides, fungicides, algicides and rotenone
(used in killing unwanted fish) (Svobodova, 1993). These
The total mercury in water for marine life culture should
chemicals are designed to be toxic and persistent, thus it
be <0.05 mg l .
is also of concern in aquaculture. It can affect the quality
-1
of the aquaculture product as well as the health of the
Lead
Lead (Pb) comes from deposition of exhaust from vehicles
in the atmosphere, batteries, waste from lead ore mines,
lead smelters and sewage discharge. Its toxicity is
dependent on pH level, hardness and alkalinity of the
water. The toxic effect on fish is increased at lower pH
level, low alkalinity and low solubility in hard water.
fish and humans.
Pesticide can be split into seven main categories namely,
inorganic, organophosphorous, carbamates, derivatives of
phenoxyacetic acid, urea, pyridinium, and derivatives of
triazine (Dojlido and Best, 1993). Among these, the
chlorinated form is of particular concern due to its
persistence and tendency to bioaccumulate in fish and
The lead in water for marine life culture should be <0.1
shellfish. Some examples are dichloro-diphenyl-trichloro-
mg l-1.
ethane (DDT), aldrin, dieldrin, heptachlor, and chlordane.
The most common sources are agricultural run-offs,
Copper
effluents from pesticide industries and aquaculture farms.
Copper enters the environment naturally through the
The safe level of DDT group in water for marine life culture
weathering and solution of copper minerals and from
should be < 0.025 µg l-1.
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Dojlido, J., and G. A. Best. 1993. Chemistry of Water and Water
Pollution. West Sussex: Ellis Horwood Limited.
Rao, P.C.V.K. ., Kumar, P.V.H and Kumar, M. 1996. Pre-monsoon
current structure in the shelf waters off Cochin : In.
Proceedings of the Second Workshop on Scientific Results
of FORV Sagar Sampada. V.K. Pillai et al. eds. Department
of Ocean Develpoment, Govt. of India, New Delhi.pp. 1924.
Masser, P. Michael. 1997. Cage culture – site selection and water
quality. Southern Regional Aquaculture Centre Publication
No. 161.
Svobodová, Z., R. L., J. Máchová, and B. Vykusová. 1993. Water
Quality and Fish Health. EIFAC Technical Paper no. 54.
Rome: FAO.
References
Beveridge, M. 2004. Cage Aquaculture. Blackwell Publishing.
Third Edition. pp.111-158.
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Diseases of seabass in cage culture and
control measures
Sobhana, K. S.
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
sobhana_pradeep@yahoo.co.in
The cage culture of finfish, especially marine cage farming is
Diseases in Cage fish farming
becoming more popular because of the many economic
The disease types and severity are greatly influenced by
advantages associated with it. Though, operationally this has
the species of fish, the conditions in which the animals
a number of advantages, the practice is vulnerable to natural
are cultured and the husbandry management. Fish
hazards and can be affected by occurrence of diseases.
cultured in floating cages become particularly susceptible
Disease outbreaks can occur more often when fish are raised
to disease when various environmental parameters such
under intensive culture conditions and can pose problems in
as temperature, salinity, dissolved oxygen and suspended
cage culture. Increased production under high density can
particles fluctuate suddenly or widely, or following rough,
create conditions conducive to outbreaks of infectious
although often unavoidable, handling operations. Once
diseases and an increase in prevalence of parasites. Infectious
conditions suitable for pathological changes develop,
diseases in fish culture are not only augmented by waste
progress to disease in the warm water environment is
pollution, but exacerbated by crowding, handling,
rapid. Early detection of behavioral changes and clinical
temperature and biofouling. The most common fish disease
signs in the cultured animals are critical for proper
in cages is vibriosis caused by Vibrio spp. Furthermore,
diagnosis of the disease. In addition to diseases caused
abrasions cause fin and skin damage to cultured stocks.
by infectious agents, diseases and abnormalities due to
Occurrence of infection/disease may be minimized by
environmental stresses and nutritional deficiencies have
selecting good sites, proper mooring and observance of
also been recognized, which can lead to secondary
optimal stocking densities and careful handling of stocks.
infections. Certain types of physical injury are specific
Disease monitoring
Monitoring of fish stock health is essential and early
indications can often be surmised from changes in
behaviour, especially during feeding. Some indication of
disease status can be gained from examination of
moribund fish netted from the cage surface. Rapid
to caged fish, e.g., if over-stocked they may suffer from
fin and skin damage caused by net abrasion and are
susceptible to pathogenic organisms if handled without
due care. Caged marine fish are vulnerable to “red boil
disease” (Vibrio anguillarum) following routine handling
operations at polluted sites (Chua and Teng, 1980).
detection and removal of dead fish helps to prevent the
Caged fish established in coastal environments may be
spread of disease.
exposed to a wide range of pathogens. From this
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perspective, the worst sites are those in which pathogenic
or potentially pathogenic organisms exist prior to
establishment of the farm and those in which disease
organisms thrive following the installation of cages.
Facultative pathogenic organisms are often associated
with water bodies where a source of infection, such as
untreated sewage, is present. There exists a link between
trophic state and bacterial/fungal infections in fish. Chua
(1979) observed that the ectoparasitic isopod Nerocilia
sp. that attacked caged rabbit fish (Siganus rivulatus) was
more prevalent in organically enriched waters.
Infectious diseases of cage cultured fish
Generally, infectious diseases of fish are caused by virus,
bacteria, fungi and parasites.
Diseases caused by viruses
Viral diseases have not been considered to be a significant
factor in marine and brackishwater culture. However,
such disease as lymphocystis has recently become one
of the problems in seabass culture. Viral diseases in cage
cultured fish have been on the increase since the 1980’s
in East Asia and the 1990’s on south-east Asia (Nakai,
Both wild fish populations and intermediate hosts in the
1995). Virological research received a new impetus
life cycle of a fish parasite represent a risk for the fish
following the high mortality in hatchery-bred juvenile fish
farmer. Cages of salmon attract scavenging sathe
soon after being placed in sea cages. With the increasing
(Pollachius virens ) that often harbour the sea lice
awareness of virus-related diseases and with new species
Lepeophtheirus salmonis and Caligus elongatus, and
of fish being selected for culture, more reports of known
laboratory trials have clearly shown that lice can transfer
and new viral diseases are to be expected.
between host species (Bruno and Stone, 1990). In the
UK, caged fish were found severely infested with the
Viral nervous necrosis (VNN)
cestodes, Triaenophorus nodulosus and Diphyllobothrium
VNN disease has been found in all warm water marine
spp. resulting in heavy mortalities and the closure of at
environments where marine fish have been cultured in
least one farm (Wootten, 1979; Jarrams et al., 1980). The
cage environments, particularly in juvenile stages. The viral
source of infection was subsequently traced to the wild
particles are packed in the cytoplasm of retinal and brain
fish populations.
cells of affected fish. Infected fish exhibit whirling
Disease risks can be minimized by avoiding sites where a
pre-development survey reveals parasites or disease
agents to be present in the wild fish or intermediary hosts.
However, problems may still occur through the
introduction of diseased stock to the farm or the
attraction of birds and other opportunistic predators.
Epidemiological studies have revealed the importance of
management in reducing the incidence of disease and
mortality. A four year study of disease outbreaks in 11
Irish salmon farms showed that interruption of parasite
movements, lethargy, dark body colouration, loss of
balance and hyper-excitability in response to noise and
light. Mortalities are usually high and occur within a week
of the onset of first signs. Extensive spongiosis is typically
observed in the retina, brain and central nervous system.
VNNV is an RNA virus and can be detected by RT-PCR. A
PCR method based on the sequence of the virus coat
protein genome (RNA2) was used to diagnose the virus in
spawners, suggesting vertical transmission of the
infection.
life cycles through fallowing, the separation of year classes
At present there is no known method of therapy, but
of fish to different sites and the practice of basic hygiene
vaccination using recombinant coat protein of live piscine
methods could significantly reduce the severity of disease
nodavirus in sevenband grouper, Epinephelus
outbreaks (Wheatley et al., 1995).
septemfasciatus, resulted in significantly lower mortality
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From 14 - 23 December 2009
in the virus challenge tests, indicating great potential for
environmental conditions. In south-east Asia, trash fish
protection against the virus.
used as feed may be another source of infection. A
decrease in stocking density and culling of visibly infected
Iridoviral disease
individuals are the only known measures that can be
Iridoviral disease has been reported in more than 20
adopted to reduce the impact of the disease.
marine species, from south-east and east Asia. Affected
fish become lethargic and severely anaemic. The gills are
Diseases caused by bacteria
hemorrhagic, the spleen is heypertrophic and the iridovirus
Many clinical signs of bacterial diseases of cultured marine
appears in a crystalline array in the enlarged, basophilic
fish are similar. Definitive diagnosis requires the isolation
splenic cells. Presumptive diagnosis based on Giemsa
and in vitro culture of the organisms involved. A great
staining of histological sections can be confirmed by
number of aquatic bacteria are opportunistic and under
immunoflorescence or by PCR assay.
normal environmental conditions do not cause disease,
An experimental vaccine prepared by Nakajima et al.
(1997) produced a higher survival in treated red seabream
than in control group, suggesting the possibility of
controlling the disease through vaccination.
Lymphocystis disease
Lymphocystis disease is commonly found in seabass raised
in cages especially among juveniles. It has been observed
at all temperatures in rather high salinity. Lymphocystis
is a highly contagious infection and the disease follows a
chronic course and, in general mortalities are limited. The
infected fishes recover within a few weeks of the onset
of the outbreak displaying little or no scar tissue. Although
known to infect 30 families of marine fish, in south-east
Asia, only Asian sea bass has been reported to be affected
by this disease.
becoming pathogenic only when the balance of the host/
environment is changed by elevated stocking densities,
inadequate nutrition, deteriorating water quality, rough
handling (e.g., net changing, grading) and other stress
factors.
Gram-negative bacteria
Vibriosis is the disease caused by a group of bacteria
belonging to the family Vibrionaceae. Vibrios are
ubiquitous in all marine environments and most are
facultative pathogens. The infectious disease they cause
is one of the most significant in mariculture. Diseases
caused by Vibrio sp. typically appear as ulcerative
haemorrhagic septecaemia. It occurs frequently during
periods of fluctuations in salinity, increased organic load,
or stress brought on by net changing and grading of fish.
The period following initial stocking is particularly critical.
The disease is characterized by tumour-like masses of
The clinical signs are congestion and red boils appearing
tissue on the body surface. These growths are clusters of
on the body surface and gradual darkening of the body.
extremely hypertrophic fibroblastic dermal cells.
The petechial haemorrhages usually enlarge into irregular
Occasionally internal organs can become infected.
and deep lesions, which disintegrate the skin, exposing
Diagnosis of lymphocystis disease is confirmed through
the underlying muscle, which becomes necrotic. The
histological sections and appropriate staining of the tissue
tissues surrounding the infected vent are usually reddened
lesions. The observation of the typical icosahedral virions
and inflamed. The body is completely covered by a thick
by electron microscopy offers further confirmation.
layer of mucus. Internally, there is congestion and
Horizontal transmission is the most probable route,
hemorrhage of the liver, spleen and kidney, frequently
facilitated by high stocking density and unfavorable
accompanied by the presence of necrotic lesions. The gut
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and particularly the rectum may be distended and filled
It is difficult to prevent and control the disease in the
with a clear viscous fluid.
cage environment. The standard treatment is feed
The pathogenic vibrios which have been isolated from
seabass include Vibrio parahaemolyticus, V. anguillarum
and V. alginolyticus. Good husbandry practices and
adequate nutrition are essential to prevent the
development of vibriosis. Though in the initial stages the
medicated with oxytetracycline or a bath in sodium
nifurstyrinate. However, the results are usually
unsatisfactory. A combination of freshwater treatment
and reduction of stocking density helps to reduce
mortality in affected seabass.
disease can be effectively treated with antibiotics, the
Tenacibaculum maritimum (formerly Flexibacter
use is not recommended due to the risk of development
maritimus ) is reported as the etiological agent of
of resistant strains. Prophylactic measures such as
flexibacteriosis disease in red seabream (Pargus major),
vaccines are recommended.
European seabass, Dicentrarchus labrax etc.
Pasteurellosis – Photobacterium damsela
Gram-positive bacteria
Pasteurellosis is an most important bacterial disease of
cultured maine fish which is caused by the Gram-negative
Streptococcosis
non-motile bacterium, Photobacterium damsela. This is
Streptococcosis caused by non-motile, gram-positive
a septicaemic disease with no external signs except
bacteria, Streptococcus sp. is most severe when farmed
occasional darkened spots on the body surface. A large
fish are stressed and water temperature is high. The onset
number of white spots corresponding to foci of bacterial
of the disease is related to the rapid growth of the
colonization engulfed by phagocytes are found in the
bacterium in the intestine where both extracellular and
spleen and kidney, and to a lesser extent in the liver. The
intracellular toxins are produced. The common clinical
diseased fish rapidly lose their vigour, sink to the bottom
signs are darkening of the body, erratic swimming,
of the cage and die. Ampicillin and florfenicol have been
hemorrhage in the intestine, liver, spleen, and kidney and
reported to be effective when administered in feed.
abdominal distention. Necroses of the heart, gill, skin and
However, this bacterium is known to become resistant
eye have also been reported.
to antibiotics. Vaccine preparations also give satisfactory
results.
Confirmation of the diagnosis requires culturing of the
pathogen, preferably on a blood-enriched medium.
Gliding bacterial disease/tail rot disease (Flexibacter sp.):
Control is mainly by chemotherapy. Antibiotic treatment
Tail rot disease caused by gliding bacteria of the genus
with erythromycin and spiramycin has proved effective.
Flexibacter, is one of the diseases commonly found in
Asian seabass in cages. The bacteria first gain entry
Mycobacteriosis
through damaged caudal fin, where the tissues are
The etiological agents of mycobacteriosis, Mycobacterium
gradually eroded away by the bacteria. The bacteria then
marinum cause systemic, chronic infections in fish. The
invade the muscular region, the muscles disintegrate and
disease follows a chronic course and remains
typical tail rot occurs. No pathological changes are
asymptomatic for a long time. Superficial ulcers and
normally observed in the internal organs. The disease
exophthalmia are often the only external signs. Spleen
usually affects seabass fry, 2 -3 weeks after their
and kidney however are severely affected and are enlarged
introduction sea cages.
with granulomatous lesions that appear macroscopically
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as whitish nodules. In advanced cases these lesions spread
age, host specificity, immunity and the influences of host
to liver, heart, mesentery etc.
condition also play an important part in the host reaction
to invasion by protozoa.
Nocardiosis
Nocardiosis is a chronic bacterial disease that affects both
freshwater and marine fish. Many clinical characteristics
of nocardiosis are similar to mycobacteriosis. Early signs
of infection include anorexia, inactivity, skin discolouration
and emaciation. In the late stages, nodular skin lesions
may ulcerate or extend to skeletal muscle and visceral
organs, causing abdominal distension. There is no effective
therapy for this disease. The route of infection in fish is
not known, but is probably through direct contact or
contaminated food. Clean environment is an important
factor in preventing the occurrence of the disease.
Protozoans cause harm to fish mainly by mechanical
damage, secretion of toxic substance, occlusion of the
blood vessels, depriving the host of nutrition and rendering
the host more susceptible to secondary infections. Some
of the most common clinical signs are changes in
swimming habits such as loss of equilibrium, flushing or
scraping, loss of appetite, abnormal colouration, tissue
erosion, excess mucus production, haemorrhages and
swollen body or distended eyes.
Cryptocaryon sp.
Cryptocaryon sp. is the marine counterpart of the
In addition to these more established pathogens,
freshwater Ichthyophthirius species and similarly cause
upcoming bacterial diseases potentially harmful for
the white spot diseases in marine fish. Its morphology
aquaculture species are being identified. A previously
and life cycle is quite similar to that of the “Ich”. The
unrecognized disease namely “pot belly or big belly”
surface of invaded fish reveals white pustules or numerous
disease caused by a facultative intracellular Gram-
minute, greyish vesicles which are nests of cilliates
negative bacterium has been identified. Infections with
burrowing under the epidermis. They feed on the host’s
this previously uncharacterized pathogen causes severe
cells underneath the epithelium and cause heavy irritation
visceral granulomatous lesions in Asian sea bass fry < 5 g
resulting in excessive production of mucus and finally
with an associated mortality rates of 70-80%.
completely destroying the fine respiratory platelets of the
gill filaments. On the skin, this parasitic protozoan causes
Parasitic diseases
Parasitic protozoa
considerable lesions resulting in destruction of large areas
of the epidermis. Secondary infection may complicate the
situation and the host dies. The incidence of Cryptocaryon
Protozoans are probably the most important group of
sp. in seabass showed a distinct peak during low water
animal parasites affecting fish. Many reports from all over
temperature period.
the world indicate great losses in cage culture caused by
protozoans. Environmental factors affect the
susceptibility of fish to certain protozoa. Oxygen
concentration and temperature are the factors affecting
both hosts and parasites. Since many protozoans transfer
from fish to fish through the water, fish population density
The presence of C. irritans in cage-cultured fish means
that the cages are kept in too shallow waters. If logistically
feasible, the cages should be moved in to an area where
sufficient depth and currents prevent the theronts (free
swimming infective stages) from re-infecting the fish.
is an important factor. Tremendous infestation of
Other important protozoan parazines affecting marine fish
protozoans can occur in a relatively short time where fish
cultured in cages are Trichodina sp., Brooklynella sp.,
populations are dense. Other factors such as host size,
Henneguya sp. etc.
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Parasitic helminthes
Worm diseases with the possible exception of those
produced by monogenetic trematodes have not yet
appeared to be a serious problem in seabass culture. This
Parasitic crustaceans are generally introduced along with
fish caught in the wild for culture, but several of them
are transmitted by wild fish around the cages. Prevention
is therefore difficult.
is probably due in large part to their complex life cycle
In addition to the infectious causes, diseases and
and the difficulty in completing such cycles in the culture
abnormalities due to environmental contaminants and
system. Helminthes parasites which have been found in
nutritional deficiencies have been recognized as important
seabass include monogenetic trematodes, digenetic
problems in fish culture whenever diets as well as control
trematodes, nematodes and acanthocephala.
or water quality become inadequate. Malnourishment or
undernourishment of seabass under culture can result in
Crustacean parasites
slow growth, susceptibility to diseases or death.
Crustaceans belonging to the Branchiura, Copepoda,
In Asia, trash fish are widely used as feed in cage farming
Isopoda and Amphipoda are frequently found on the body
of marine finfish. Fry are often wild caught or derived from
surface and/or gills of caged marine fish.
wild-caught broodstock. Furthermore, legislation for and
Parasitic copepods
implementation of farming licenses and zoning policies
are not in place in most Asian countries. Coupled with a
The parasitic copepods are among the most devastating
‘gold rush’ mentality, this often results in too many fish
of fish parasites. The mature female usually attaches to
and too many farms in a concentrated area, which in turn
the fish and feeds on the host. After copulation the female
promotes disease transmission. The combination of all
matures and produces egg sacs while the male dies.
these factors, together with the diversity of organisms in
The only branchiuran reported is Argulus sp. Most of the
tropical waters, leads to a truly challenging disease
copepods reported are caligids, which could cause epizootics
situation.
in the farms. Caligus sp. has caused big problems in cultured
Furthermore, irresponsible use of antibiotics and
seabass. They attach to the gills, buccal and opercular
chemicals for disease control in aquaculture can lead to
cavities, occasionally on the skin and fins of the seabass.
residue problems, an increasing consumer concern, and
Heavy infections can cause mass mortalities especially in
to the development of drug resistance among the bacterial
young fish. Lernanthropus sp. are found attached to the gill
pathogens. In addition to developing antibiotic resistance,
of seabass especially in cage cultured fish. Large numbers
sick fish often do not eat and the efficiency of delivering
of this parasite can cause anaemia to the fish host.
antibiotics orally is often questionable. The use of
Parasitic isopods
antibiotics is a curative measure to treat an existing
infection; in contrast, vaccination is a preventative
Isopods which closely resemble Aega sp. have been found
measure, dependent on the immune system of the animal.
abundant in cage-cultured seabass. The parasite always
Vaccines can act against bacterial, viral and, at least
attaches to the gills of its host. Clinical signs of infected
experimentally, parasitic infections and they will usually
seabass are as follows: fish lose appetite, become anemic
act only against the targeted pathogens. In Asia, with
and grow very slowly. Quick death can occur in 2–3 days
the exception of Japan, few fish vaccines are yet
in heavily infected young fish. Nerocila sp. and Gnathia
commercially available. The major advantages of
sp. have also been reported in seabass.
prophylactic vaccination over therapeutic treatment are
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that vaccines provide long-lasting protection and leave
diseases has become more and more important in the
no problematic residues in the product or environment.
cultivation of aquatic animals. Good health management
Asian aquaculture will continue to grow at a fast pace
is the best way for disease control. Collectively, this
due to both area expansion and production intensification.
includes the use of healthy fry, quarantine measures,
Under these conditions, the prevalence and spread of
optimized feeding, good husbandry techniques, disease
infectious diseases will unavoidably increase as a result
monitoring (surveillance and reporting), and sanitation as
of higher infection pressure, deterioration of
well as vaccination, and biosecurity measures when
environmental conditions and movement of aquatic
diseases do occur. Overall, the emphasis must be on
animals. Accordingly, the effective control of infectious
prevention rather than treatment.
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Open sea cage culture in IndiaA sociological perspective
Ramachandran, C.
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
ramchandrancnair@gmail.com
Introduction
Marine cage culture is the latest innovation in Indian
mariculture scenario. The first cage was demonstrated in
Visakhapatanam in 2007-08. The logic of the floating cage
culture technology is the conversion of marine space into
a controlled production system. This entails a number of
socio-political issues apart from the technological ones.
mature industry in these countries (Grottum and
Beveridge 2007). In the Asian region, China has
attained significant strides in off shore cage culture.
Within the span of a decade (1990-2000) and with an
investment of more than US$10 million, China has
deployed about 4000 such cages yielding about 2 lakh
tons ( Chen and Chen 2008).
Prominent among them is the changing context of marine
India’s entry into the arena of off shore cage culture is
tenure in the country. This paper analyses such issues
very recent and this marks a significant milestone in the
based on a preliminary study conducted in some of the
mariculture pursuits of the country. The history of
locations where the cage demonstration has been
mariculture research in India dates back to early seventies
implemented. The major sociological framework employed
when pioneering attempts were made by CMFRI to farm
in the analysis is that of the Actor –Network Theory (ANT)
mussels in the inshore waters using lines. Though the
proposed by Latour (2007). Thus the methodological
technology was successfully demonstrated, it did not
objective was to explore the actor- networks at different
capture the imagination of the fisher folk for reasons
locations using participatory protocols.
obvious. The major stumbling block was the absence of a
“culture mindset” which was partly due to resource
The idea of cultivating fish in the open sea through
abundance amenable to exploitation through capture
cages is of recent origin. Open sea cage culture is being
fisheries. With the capture fisheries production leveling
posed as an answer to increasing demand for food in
off in the recent years the potential for the open sea cage
the context of the declining yield trend shown by
culture is huge.
capture fisheries (especially when the Chinese catch
Visakhapatanam has come as a shot in the arm to our
excluded) and the problems faced by the land based –
mariculture aspirations.
aqua farming technology. The pioneers in this
technology are countries like Norway, Japan and USA.
The success demonstrated at
Objective and methodology
After about three decades of intense research and
It is in this context that the present study was undertaken
development activities cage culture has become a
to assess the perception of the stakeholder constituency
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and to reflect on the challenges and prospects of open
mainly determined by innovation characteristics (as
sea mariculture. The cage culture is a newly introduced
defined by Rogers, 2003) only can be assessed now.
innovation and could be either adopted or rejected by the
stakeholders. An individual’s decision to adopt or reject
a new practice passes through several stages, and does
not happen at once. Innovation diffusion studies have
recognized the adoption/non-adoption of a new
introduced practice is influenced by whether or not it
matches with the adopters’ needs, situation, and
perceptions of the innovation (Rogers, 2003).The rate of
adoption might differ among individuals depending on his/
The location of the sites where the preliminary study was
conducted is depicted in Table1. It also shows the current
status of the culture in these sites. As it can be seen
some of the sites one demonstration was over and in other
places the first series of demonstration was in different
stages of operation. There was continuous access to all
the operations at Munambam which was covered during
(9/12/08 to 18/04/09).
her level of innovativeness. The more innovative an
A notable feature of the innovation transfer model being
individual the shorter is the adoption time. Since the
attempted across the sites is the way in which the various
innovation is in the nascent stage of adoption it is not
agencies and institutions are integrated. The dominant
possible to draw of picture of its diffusion. The perception
mode is that of Public-Private Partnership. The table below
of people on the probability of its adoption, which is
gives an over all view on this aspect.
Table 1
Sites of open sea cage culture visited
Site
State,district
Distance from cmfri centre
Status of cage
remarks
1. ChaumukhBaliapal
Orissa,
Baleswar/
Balasore
From Viskah,
about 700km
Cage installed in the sea, Very good cooperation from
4000 fingerlings of sea
the fisheries department and
bass stocked
the fisher folk
2.Visakhapatanam
AP, Visakah
About 5km
Second cage P monodon
stocked
3.Iskapalli
AP, Nellore
About 200 km from Chennai -Two cages installedModifications done to
stock P. monodon and
lobsters
Fisher folk evince keen
interest
4.Pulikat
Tamil Nadu,
About 50 km from Chennai
Ready for stocking
lobsters Good support
from the
NGO and fisher folk.
Fishers more interested
as this is the second time
5.Munambam
Kerala
About 30 km from Kochi
Harvest done
Pre mature harvest due to
drifting of cages; growth
parameters promising
6.Vizhinjam
Kerala
About 18 km from Thiruvananthapuram
Table 2
The fishermen group has
gained more confidence
Harvest done
Modes of institutional arrangements
Site
Mode
ChaumukhBaliapal(orissa)
PPP
Society of the traditional fisherfolk+State Department of Fisheries+CMFRI+NFDB
Details
Visakhapatanam (AP)
do
Fishermen society +lead role by a fisherman leader+DF+CMFRI+NFDB
Iskapalli,Nellore(AP)
do
Fishermen society +lead role by a fisherman leader + DF+ CMFRI+ NFDB
Pulikat, Chennai ( TN)
do
Fishermen society +NGO +DF+CMFRI+NFDB
Munambam
Fishermen group +CMFRI+NFDB
Vizhinjam
do
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fund of the Government. In Balasore, the group was willing
Perception of stakeholders
Perceived attributes of an innovation such as relative
advantage, complexity, compatibility, trialability, and
to put operational expenditure provided the cage was
given to them.
perceived risks have been used extensively in previous
It is to be noted that the demonstration is just in progress
innovation studies to evaluate innovation adoption.
in Balasore. Nevertheless the stakeholders here have a
(Rogers 1983) defines relative advantage as ‘the degree
much more favorable perception towards the innovation.
to which an innovation is perceived as being better than
This could be because of certain socioeconomic
the idea it supersedes’. Complexity is defined as ‘the
peculiarities of the village like backwardness, homogeneity
degree to which an innovation is perceived as relatively
of the group, and the presence of a culture mindset owing
difficult to understand and use’]. Trialability is defined as
to the fact that almost all the fishermen families possess
‘the degree to which an innovation may be experimented
farm lands for cultivation. The fishermen in the west coast
with, on a limited basis’ Compatibility is defined as ‘the
( represented by two sites) was found to be a bit reserved
degree to which an innovation is perceived as consistent
as only medium response was obtained on this count. This
with the existing values, past experiences, and needs of
must be read in tandem with their perception on innovation
potential adopter’. Perceived risk is defined as the degree
characteristics which was found to be low on
to which an innovation is perceived to be economically
risky.
Another remarkable observation is the increase in level
of confidence shown by the fisherfolk after the
The stakeholders in general showed enthusiasm towards
the innovation in all the locations. Though this is
encouraging it needs to be qualified with the facts that
the demonstrations are being carried with financial
support to the stakeholders. But the real litmus test is
their willingness to adopt the innovation entirely on their
own. When this question was asked on a Likert type scale
the responses obtained were revealing. The * sign
indicates the perception before the demonstration and $
indicates the same after the demonstration.
Visakahpatanam was found to be more positive on this
count.
demonstration of the technology in one season.
When the perceived innovation characteristics were
considered the pattern obtained has been deputed below.
The response was not collected from the two places where
the demonstration was not completed. The innovation
characteristics registered a better perception in
Visakhapatanam. This could be due to many facts like
a) the positive impact due to the success of the first
demonstration
b) the role played by Mr Polanna who happen to be the
leader of a state level fishermen association
Table 3 Perceived adoptability across locations
1(Blsr)
High
Medium
2(vsk)
3(nlr)
4(plkt)
5(mnmbm)
6(vzj)
$
$
$
*
*
*
*
$
*
*
Low
(High-above 75% of response, Medium-50-75% Low –below 50%)
Though high initial cost is a perceived deterrent across
the locations, the Visakhapatanam group was optimistic
to get financial assistance through the Tsunami assistance
c) better accessibility to technical advise and supervision
from CMFRI
d) higher innovativeness of the group
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Table 4 Perceived innovation characteristics
Innovation characteristic
1(Blsr)
2(Vsk)
3(Nlr)
4(Plkt)
5(Mbm)
6(Vzj)
Relative advantage ( high)
$$$
$
$
$
Complexity ( low)
$$
$
$
$
Trialability ( high)
$$$
$$
$
$
Compatibility ( high)
$$$
$$
$
$
Perceived risk( low)
$$
$
$
$
($$$-above 75% Agree, $$-50-75% Agree,$-less than 50% agree)
Prospects and Challenges
Though it is too early to comment on the future of the
innovation in the Indian scenario some reflections made
in this direction seems not to be out of place. The question
is will the technology get adopted and diffused? The
answer depends on three major factors a) technological
b) socio-economical and c) political/governance. Since the
technological factors are being addressed by the
concerned persons I limit my discussion to the sociological
and political aspects here.
Sociological factors
The major factor that influences the innovation decision
process is the extent to which the candidate innovation
meter. Another factor is the price they get for the cagecultured fish. Though high value fishes are being
recommended now, their price is dependent on the market
vulnerability. Another factor is the delay in the financial
reward. Unlike capture they have to wait for about five
to six months for the harvest. But compared to the former,
cage culture is less risk prone. But fishermen were of
the opinion that if the season of the culture is planned in
such a way that the harvest synchronizes with the lean
season/high demand season like festivals they could earn
better price. Since cage culture offers control over the
production system possibilities of getting premium price
by way of organic certification or other certifications could
be explored.
meets the felt needs of the incumbent adopter. The
Though threats like poaching or community-agreed
relative advantage of this innovation has been favouarbly
vandalism are real they can be remedied if the community
perceived. The fisher folk in general feel that the capture
is vested with the ownership of the cages. Innovativeness
fisheries sustainability is in peril and they are in the look
of the fisherfolk need to be tapped to the maximum extent
out for alternative livelihood sources. It can be assumed
possible in all the aspects like selection of sites, species,
that the cage culture in this aspect has captured their
feed, cost cutting strategies etc.
imagination if one goes by the enthusiasm shown by the
people. The emergence of a culture mindset is a welcome
sign because fishermen are believed to be still in the
hunter- gather mindset.
Political/governance factors
The cage culture being a point of departure against the
conventional sense of marine tenure it poses many
There are push and pull factors behind the adoption of
challenges in this regard. To established ocean users cage
any innovation. One of the major deterrents is the
culture is a new system of property that regulates access
perceived high initial cost. But if the cages are made
and usage of marine resources. Until recently the ocean
available to the fishermen group at a subsidized cost it is
was considered to be the last of the commons, where
well likely to be adopted. Attention needs to be given to
ownership is based on the labour that fishermen invested
cost cutting strategies in the cage fabrication. The cost
in the act of catching them. The marine tenure system
of HDPE cages in China is said to be only Rs600/cubic
prevalent in the country, though its enforcement is feeble,
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grant rights to fishing territories they do not guarantee
surmount. No social scientist who has ever experienced
that fish would not migrate out of these territories. Until
the frustrating pangs of establishing a “connection “ with
a fish is caught nobody is considered to be a legitimate
the fisherfolk can fail to see the transformation of cages,
owner of that fish. The concept of cage culture thus marks
with its positive image of being a tangible production
a significant departure from this notion. So the need of
system innovation, as becoming emotional bridges.
the hour is to chalk out a suitable marine property rights
policy giving due weightage to the rights of the community
Concluding remarks
but not forestalling socially committed corporate bodies
It is too early to predict the future of the cage culture in
in entering the scenario on a Public Private Partnership
India. The innovation has many challenges as well as
mode. A system of Public hearing as has been practiced
opportunities. To tackle the challenges a great deal of
in Hawai ( Suryanata and Umento 2002) could be followed
discussion, planning and coordination is required to create
in legitimizing commercialization of marine space.
dynamic networks on a value chain basis. However its
fate lies in the collective will, social capital and
Cage as a new metaphor
institutional capacity of a number of agencies and
There is nothing more puzzling than a proposition that
institutions involved. The lessons from the countries who
views Open Sea Cages as bridges! But this is the
are ahead of us could be of much use in terms of not only
concluding remark I would like to pose. Yes, the cages
the technology but also the marine farming governance.
have started acting as socio-psychological bridges
The demonstrations being undertaken in different parts
between the marine fisheries R&D and the fisherfolk along
of the country needs to be viewed in the perspective of
the coast of this country. The Indian coastal villages never
Multi Locational Trials and there is an urgent need to
had such a “bridge’ built through their collective psyche,
convert such collective knowledge into location specific
except perhaps the few mariculture interventions done
policies, norms, networks and practices.
in the late seventies. There always has been an intangible
barrier between the fishermen and the kind of scientific
knowledge, (especially the stock assessment knowledge
which is the main mandate of CMFRI) that has been
generated by the researchers. Being relevant only at a
wider policy level, there is no wonder that, this knowledge
base could hardy capture the imagination of the fisherfolk.
They often found the research system as an anathema,
informing governments to make policies that went against
their immediate interests (like mesh size regulations/
reduction in fishing effort/even the seasonal fishing bans).
The scientific advice was deemed to be with a touch of
inherent negativity. This has led to the development of
an annoying sense of mistrust among the fisherfolk and
this has been the biggest communication barrier an
extension scientist working in the marine sector has to
References
Chen J , Xu, H. and Chen Y., 2008. Marine fish cage culture in
China. In A. Lovatelli, M.J. Phillips, J.R. Arthur and K.
Yamamoto. (eds). FAO/NACA Regional Workshop
ftp://ftp.fao.org/docrep/fao/011/i0202e/i0202e14.
Grottum J. A. and Beveridge,M., 2007. A review of cage
aquaculture .Northern Europe. In M Halwart,D ,Soto and JR
Arthur (eds).Cage Aquaculture-regional reviews and global
overview. FAO Fisheries Technical paper no 498:126-154.
Latour, Bruno, 2007. Reassembling the social-An introduction
to Actor- network theory. Oxford University Press.pp301.
Rogers, E. M., 1983.Diffusion of innovations. Free Press , New
Ypork.pp550
Suryanata, K. and Umemeotot,K., 2002. Capturing fugitive
resources in a globalised economy: the case of marine
aquaculture in Hawai.dlc.dlib.indiana.edu/archive.
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Grow out culture of seabass in cages
Boby Ignatius
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
bobycmfri@yahoo.co.in
Aquaculture of Lates calcarifer, known as seabass, was
small coastal cage farms. Often these farms will culture
commenced in the 1970s in Thailand, and rapidly spread
a mixture of species, including Seabass, groupers (Family
throughout Southeast Asia. In India also it is a sought
Serranidae, Subfamily Epinephelinae) and snappers (Family
after fish in many states. The grow-out phase involves
Lutjanidae). Australia is experiencing the development of
the rearing of the seabass from juvenile to marketable
large-scale Seabass farms that reflect the industrialized
size. Marketable size requirement of seabass vary country
style of aquaculture seen in Europe, where Seabass
to country e.g. in Malaysia, Thailand, Hong Kong and
farming is undertaken outside the tropics, recirculation
Singapore, the normally accepted marketable size of
production systems are often used (e.g. in southern
seabass is between 700–1200 g while in the Philippines,
Australia and in the north-eastern United States of
marketable size is between 300–400 g. The culture period
America).
in grow-out phase also vary from 3–4 months (to produce
300–400) to 8–12 months. The success of marine cage
culture of seabass and its economical viability have
contributed significantly to large scale development of
this aquaculture system
Most seabass grow out is undertaken in net cages. The
cages are either floating or fixed and range in size from 3
x 3 m up to 10 x 10 m and 2 -3 m deep. The mesh sizes of
these cages ranges from 2-8 cm. Seabass are reared from
juvenile to marketable size varies depending on water
Among the attributes that make Seabass an ideal
quality and the environmental conditions of the culture
candidate for aquaculture are:
site. Floating cages can be stocked more than stationary
z
z
It is a relatively hardy species that tolerates crowding
cages. This is because floating cages are usually set in
and has wide physiological tolerances.
sites with better aquatic environmental conditions such
The high fecundity of female fish provides plenty of
material for hatchery production of seed.
as deeper water, smaller fluctuation of water salinity,
more rapid circulation and further away from sources of
pollution.
z
Hatchery production of seed is relatively simple.
z
Seabass feed well on pelleted diets, and juveniles are
Suitable site for seabass cage culture
easy to wean to pellets.
Criteria for selecting a suitable site for cage culture of
Seabass grow rapidly, reaching a harvestable size (350
seabass include:
z
g – 3 kg) in six months to two years.
a. Protection from strong wind and waves. The cage
Today Seabass is farmed throughout most of its range,
culture site should preferably be located in protected
with most production in Southeast Asia, generally from
bays, lagoons, sheltered coves or inland sea.
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b. Water circulation. The site should preferably be located
Stocking density in cages is usually between 40–50 fish
in an area where influence of tidal fluctuation is not
per cubic meter. Two to three months thereafter, when
pronounced. Avoid installing cages where the current
the fish have attained a weight between 150–200 g, the
velocity is strong.
stocking density should be reduced to 10–20 fish per
c. Salinity. Suitable site for seabass culture should have
a salinity ranging from 13–30 ppt.
d. Biofouling. The site should be far from the area where
biofoulers abound.
cubic meter. Generally, increase in densities results in
decreased growth rates. Higher stocking densities require
more monitoring of water quality and fish health,
additional aeration and higher water exchange rates.
e. Water quality. The site should be far from the sources
There should be spare cages as these are necessary for
of domestic, industrial and agricultural pollution and
transfer of stock and to effect immediate change of net
other environmental hazards.
in the previously stocked cage once it has become clogged
The optimum temperature for Seabass culture is 28°C,
with acceptable growth rates between 26-30°C.
Temperatures below this range will result in decreased
metabolism and growth. Seabass generally stop feeding
at temperatures below 20°C. At optimum temperatures,
with fouling organisms. Changing cages allows for grading
and controlling stock density.
The choice of netting mesh size of fish
Mesh size
Size of fish
0.5 cm
1–2 cm
1 cm
5–10 cm
12 months.
2 cm
20–30 cm
The water quality parameters which are considered of
4 cm
bigger than 25 cm
Seabass can be raised to market size (500g) between 6-
minimum range for cage culture of seabass
The suitable water quality for cage culture of seabass.
Parameters
Ranges
Feeds and feeding
Due to the carnivorous nature of Seabass, a high protein
diet is required for efficient growth. Commercial diets are
pH
7.5–8.3
Dissolved Oxygen
4.0 – 8.0 mg/L.
Water salinity
10 – 31 ppt.
Water temperature
26 – 32 °c
Ammonia — nitrogen
less than 0.02 mg/L.
of 1.5-2:1 (kg of food: kg of weight growth), however lower
Hydrogen sulfide
none
FCRs have been reported by some industry members.
readily available from a number of feed manufacturers and
are generally produced in a floating or sinking pellet. Food
conversion ratios (FCRs) for Seabass should be in the range
The stocking densities used for cage culture generally
Trash fish is the main feed for seabass culture. Trash fish
range from 15 to 40 kg/m³, although densities may be as
should be fresh and clean. Trash fish used in Thailand are
high as 60 kg/m³. Prior to stocking seabass juvenile in
sardines and other small marine fish. The trash fish should
cages, fish should be acclimatized to the ambient
be chopped and fed twice a day, in the morning and
temperature and salinity prevailing in the cages. The fish
afternoon. The size must be suitable for the size of the
should be graded into several size groups and stocked in
mouth of the fish. The farmers should give the feed slowly
separate cages. The stocking time should be done in the
and watch the fish. Feeding should be stopped when the
early mornings (0600–0800 hours) or late in the evening
fish no longer come up to the surface; it shows that the
(2000–2200 hours) when the temperature is cooler.
amount of feed is enough for them.
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
Feed is the major constraint confronting the seabass
culture industry. At present, trash fish is the only known
feed stuff used in seabass culture. Chopped trash fish are
Monthly growth (g) of seabass at different stocking densities in
cages ( Sakaras, 1982)
Culture Period
16/m
Stocking density
24/m
32/m
given twice daily in the morning at 0800 hours and
0
afternoon at 1700 hours at the overall rate of 10% of total
1
biomass in the first two months of culture. After two
2
months, feeding is reduced to once daily and given in the
3
262.9
afternoon at the rate of 5% of the total biomass. Food
4
326.2
332.0
311.5
5
381.1
384.9
358.8
6
498.6
487.1
455.4
should be given only when the fish swim near the surface
to eat. Vitamin premix may be added to the trash fish at
67.8
67.8
67.8
132.3
137.5
139.2
225.2
229.1
225.5
267.5
264.1
a rate of 2 percent, or rice bran or broken rice may be
Main problem in grow out culture are feeding and
added to increase the bulk of the feed at minimal cost.
prevention of cannibalism in young fishes. In order to
Food conversion ratios (FCRs) for Seabass fed on trash
reduce losses due to cannibalism, grow out is performed
fish are high, generally ranging from 4:1 to 8:1.
in two phases, viz. nursery phase up to a size of 20g in
Growth
nursery ponds/cages and grow out phase The size of the
feed must be suitable for the size of the mouth of the
Growth is highly variable and depends on various factors
fish. The farmers should feed fish slowly and watch them.
including temperature, feeding rate, feed quality and
Feeding should be stopped when the fish no longer come
stocking density. Generally fish grows from fingerling to
up to the surface which indicates that the amount of feed
300-500g in 6-12 months and to 3kg in 2 years.
is enough for them. Food conversion rates of seabass also
Stocking larger size seed fish attains greater individual
depend on the quality and quantity of trash fish. Normally,
and total weight per cage than smaller ones. Seabass size
seabass can grow at an average of I kg/yr. Survival rates
ranges from 10-17cm in length are suitable for culturing
for marketable fish culture are about 80-95 percent in
in cages with grow out at 6- 7 months.
normal culture conditions.
101
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Open sea Cage culture: carrying capacity
and stocking in the grow out system
Shoji Joseph
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
sjben@yahoo.com
Developing open sea cage farming is a new way of
the environment can sustain indefinitely, given the food,
providing employment to fishermen transferring from fish
habitat, water and other necessities available in the
capture to aquaculture. It will also create significant socio-
environment. In ecological terms, the carrying capacity
economic influences in the future. The near target of cage
of an ecosystem is the size of the population that can be
culture is that marine fish farming will become a main
supported indefinitely upon the available resources and
force in aquaculture sector. The open sea cage culture
services of that ecosystem. Living within the limits of an
has been expanding in recent years on a global basis and
ecosystem depends on three factors:
it is viewed by many stakeholders in the industry as the
z
the amount of resources available in the ecosystem
aquaculture system of the millennium. The Asian seabass,
z
the size of the population, and
Lates calcarifer, known as “Kaalangi” in Kerala is an
z
the amount of resources each individual is consuming.
important candidate finfish species for sea cage farming.
Carrying capacity
A major consideration in the site selection process should
be the carrying capacity of the site which indicates the
maximum level of production that a site might be expected
to sustain. Intensive cage fish farming results in the
production of wastes which can stimulate productivity and
alter the abiotic and biotic caracteristics of the water body,
whilst less intensive methods can result in over croppping
of algae and a fall in productivity. Hence profitability or
even viability may be seriously affected. Therfore it is
extremely important for all concerned with cage fish
farming to have an accurate evaluation of the sustainbale
levels of production at a particular site before culture.
A simple example of carrying capacity is the number of
people who could survive in a lifeboat after a shipwreck.
Their survival depends on how much food and water they
have, how much each person eats and drinks each day,
and how many days they are afloat. If the lifeboat made
it to an island, how long the people survived would depend
upon the food and water supply on the island and how
wisely they used it. A small desert island will support far
fewer people than a large continent with abundant water
and good soil for growing crops. In this example, food
and water are the natural capital of the island. Living
within the carrying capacity means using those supplies
no faster than they are replenished by the island’s
environment: using the ‘interest’ income of the natural
capital. A community that is living off the interest of its
The carrying capacity of a biological species in an
community capital is living within the carrying capacity.
environment is the population size of the species that
A community that is degrading or destroying the
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
ecosystem on which it depends is using up its community
Feed losses are inevitable during fish culture for a number
capital and is living unsustainably. So, in the context of
of reasons; but the left over food that is not be eaten is
sustainability, carrying capacity is the size of the
actually not a loss in the culture systems; instead
population that can be supported indefinitely upon the
contribute to the wastes from the operation.
available resources and services of supporting natural,
Manufacturers estimate that 2% of feed is ‘dust’, due
social, human, and built capital.
largely to the crumbling of pellets during packing and
Within the context of aquaculture, environmental carrying
capacity is defined as the maximum number of animals
transport and thus at least 2% of commercial feeds will
be uneaten and contributes to the water body.
or biomass that can be supported by a given ecosystem
In order to determine the potential of a water body for
for a given time. This is particularly important to
intensive enclosure, the productivity of the same prior to
aquaculturists who seek to optimize the economic value
exploitation must be assessed through measurement of
or yield per unit area, or regulatory authorities who are
the steady-state total-P concentration, The development
interested in minimizing the negative impacts aquaculture
capacity of a lake or reservoir for intensive cage and pen
can have on the natural environment through the issuing
culture is the difference between the productivity of the
of permits or granting concessions.
water body prior to exploitation, and the final desired level
Estimation of Carrying capacity
of productivity. As stated above, [P] can be used as a
productivity indicator. However, it must be decided
In semi-intensive and intensive systems the number of
whether it is then mean annual algal biomass, or the peak
fish that may be stocked will be limited by the “carrying
annual algal biomass, as measured by chlorophyll levels
capacity” of the water. This can be calculated using
[ch1] and [ch1]max respectively, that we wish to predict.
standard methodology. Before considering how to model
Since fish are usually held in cages throughout the year,
the impact of cage fish culture on the environment, the
it is the latter parameter which should be considered.
rationale behind using this method to increase fish
production should be understood. The modeling is based
The capacity of a water body for intensive cage and pen
on the assumptions that algal population densities are
fish culture is the difference, Ä [P], between [P] prior to
negatively correlated with water quality in general and
exploitation, [P]i, and the desired/acceptable [P] once fish
growth and survival of fish stocks in particular, and that
culture is established, [P]f.
phosphorus (P) is the limiting nutrient which controls
phytoplankton abundance in the water bodies.
I.e. Ä [P] = [P]f - [P]i
Phosphorus and, occasionally, light are the principal
Ä[P] is related to P loadings from fish enclosures, Lfish, the
factors limiting production, and thus the net addition or
size of the lake, A, its flushing rate, ñ, and the ability of
uptake of P or materials which greatly influence the light
the water body to handle the loadings (i.e. the fraction of
climate will alter productivity. Phosphorus is an essential
Lfish retained by the sediments, Rfish):-
element required by all fish for normal growth and bone
development, maintenance of acid-base regulation, and
lipid and carbohydrate metabolism. Diets deficient in P
can suppress appetite, normal food conversion and
growth, and under extreme circumstances affect bone
formation and lead to death.
103
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
The acceptable/desirable change in [P], Ä [P] (mg m-3), is
Here nitrogen and phosphorus are the water quality
determined as described above, and z can be calculated
parameters considered for the calculation of carrying
from hydrographic data obtained either from literature or
capacity. The simulated results showed the maximum
survey work:-
nitrogen and phosphorus concentrations were 0.216 mg/
Where V = volume of water body (m3) and A =
surface area (m2) the flushing rate, (y-1) is equal to Qo/V,
where Qo is the average total volume out flowing each
year. Qo can be calculated by direct measurement of
outflows, or in some circumstances can be determined
from published data on total long-term average inflows
from catchment area surface runoff (Ad.r), precipitation
(Pr) and evaporation (Ev), such that
Qo = Ad.r + A(Pr - Ev) (see Dillon and Rigler, 1975, for
further details).
L and 0.039 mg/L, respectively. In most of the sea area,
the nutrient concentrations were higher than the water
quality standards. The calculated environmental carrying
capacity of nitrogen and phosphorus in Xiangshan Harbor
were 1,107.37 t/yr and 134.35 t/yr, respectively. The results
showed that the waste generated from cage culturing in
2000 has already exceeded the environmental carrying
capacity.
Unconsumed feed has been identified as the most
important origin of all pollutants in cage culturing
systems. It suggests the importance of increasing the feed
The retention coefficient, R, can be determined
utilization and improving the feed composition on the
experimentally by measuring the mean annual inflow and
basis of nutrient requirement. For the sustainable
outflow [P], [P]i; and [P]o respectively:-
development of the aquaculture industry, it is an effective
management measure to keep the stocking density and
pollution loadings below the environmental carrying
Marine cage aquaculture produces a large amount of waste
that is released directly into the environment. To effectively
manage the mariculture environment, it is important to
determine the carrying capacity of an aquaculture area. In
many Asian countries trash fish is dominantly used in
marine cage aquaculture, which contains more water than
pellet feed. The traditional nutrient loading analysis is for
pellet feed not for trash fish feed. So, a more critical
analysis is necessary in trash fish feed culturing areas.
Based on the hydrodynamic model and the mass transport
model in Xiangshan Harbor, the relationship between the
water quality and the waste discharged from cage
aquaculture has been determined. Here corresponding to
FCR (feed conversion ratio), dry feed conversion ratio
(DFCR) was used to analyze the nutrient loadings from
capacity.
The DFCR-based nutrient loadings analysis
indicates, in trash fish feed culturing areas, that it is more
critical and has been proved to be a valuable loading
calculation method. The modeling approach for Xiangshan
Harbor presented here is a cost-effective method for
assessing the environmental impact and determining the
capacity. Carrying capacity information can give scientific
suggestions for the sustainable management of
aquaculture environments. It has been proved that
numerical models were convenient tools to predict the
environmental carrying capacity. The development of
models coupled with dynamic and aquaculture ecology
is a requirement of further research. Such models can also
be useful in monitoring the ecological impacts caused by
mariculture activities.
marine cage aquaculture where trash fish is used. The
Fish stocking in the cages
environmental carrying capacity of the aquaculture sea
The minimum recommended stocking density for common
area can be calculated by applying the models noted above.
carp, tilapia, and catfish is 80 fish/m3. A recommended
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
maximum stock density for beginning farmers is the
cage(s) to assure that the weight does not reach the
number of fish that will collectively weigh 150 kg/m3
carrying capacity of the water body during culture.
when the fish reach a predetermined harvest size
(Schmittou, 1991). The smallest recommended fingerling
Maximum volume of cages (m3) = 2.6a*
Where: a
= total surface area of water
body (1,000s of m2)
size for stocking is 15 g. A 15-g fish will be retained by a
13-mm bar mesh net. Larger fish can also be stocked into
* The constant 2.6 is derived below
cages. Survival rates in well-placed and well-managed
400 kg
cages are typically 98 to 100 %. Unless greater mortality
1,000 m2 pond
is expected, no adjustment is needed to calculate stocking
150 kg
density. An example of how to calculate the number of
fish to stock per cage follows: Assume that a farmer wants
harvest fish weighing 500 g from a 1m3 cage.
m3 cage
Grow out of the sea bass culture starts as it transfers to
Total fish weight at harves
t= 150 kg/m
3
the cages from the nurseries. Juveniles of sea bass reared
Number to stock
= 300 fish (300 x0.5kg)
in the nurseries of size 10 - 15 cm in length (25 – 50 g in
Desired average fish weight
= 0.5 kg at harvest
Production
= 150 kg/m3
wt) can be transferred to the cage for the grow-out. The
For a harvest of fish averaging 200 g, the number of fish to
stock would be:
Number to stock
= 750 fish/m
0.2 kg x 750
= 300 kg/m
3
3
The carrying capacity of a body of water limits the weight
of fish that can be cultured. Stocking so many fish that
the carrying capacity is exceeded will result in increased
stress, disease, and mortality, and reduced feed
stocking density in the cages varies from 20 – 25 kg/m3
in the final harvest time. So with a final weight of
expectation of 1 kg fishes in harvest time after a period
of 6 – 8 months; from the cages the stocking density
varies from 25 – 30 fishes / m3 for the sea bass. Care
must be taken to avoid handling stress and other
physiological stresses as maximum as possible while
transport and stocking.
conversion efficiency, growth rate, and profit. Generally,
Once when the carrying capacity is determined in a culture
1,000 m of water surface area is needed to support 400
system, and optimum stocking is done accordingly, open
kg of fish. A calculation can be used to determine the
sea cage culture can be a successful alternative for any
maximum number of fish which can be stocked into a
species of high value marine fish.
2
105
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Growth in fleet size and investment in marine
fisheries and scope for open sea mariculture
Sathiadhas, R.
Central Marine Fisheries Research Institute, Post box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
rsdhas@rediffmail.com
Fishing has been considered as a primary livelihood option
sea mariculture by adopting location specific appropriate
since time immemorial, for the occupants of the coastal
technologies.
belt in India, stretching along 8129 kms. Fisheries play a
predominant strategic role in the economic activity of
our country by its contribution to national income, food
and employment. It supports the deprived coastal
community and serves as an important foreign exchange
earner contributing substantially to food and nutritional
security. It is also a principal source of livelihood to people
in coastal areas. Fisheries contribute about 1 per cent of
India’s GDP, which forms about 4.12 per cent of the
agricultural GDP (2003-04). The total fish production
The backdrop of fisheries legislations enacted in India
traces back to 1857, when the Indian Fisheries Act was
endorsed. It was meant to regulate riverine fisheries and
fisheries in inshore waters, to prohibit the use of poisons
and dynamite in fishing, and to protect fish resources in
selected waters through regulation of, among other
things, the erection and use of fixed engines (the reference
is to nets, cages, traps, etc.), the construction of weirs,
the use of nets of certain types and dimensions, etc.
during the four decades (1950-51 to 1990-91) showed an
The present day scenario is governed by various sets of
annual average compound growth rate that varied
enactments essentially having bearing on the marine
between 3.35 to 4.62 percent. About 12.2 lakh fisherfolk
fisheries sector. These legislations include Maritime Zones
operate diverse types of craft-gear combinations with
Act (1976) which recognizes the sovereign rights to
regional and seasonal variations all along the Indian
conservation and management of living resources in the
coastline. The secondary sector provides employment to
Indian EEZ, in addition to their exploration and
more than 15 lakh people and another one lakh people is
exploitation. Another important regulation governing the
employed in the tertiary sector. Decline in catch rates
marine fisheries is Maritime Zones of India (Regulation of
coupled with increasing domestic and international
Fishing by Foreign Vessels) Act (1981) and Rules (1982).
demand of high value species has resulted into more
Fisheries within the 12-mile territorial limits are managed
conflicts in sharing of resources, increase in migration of
under the Marine Fishing Regulation Acts (MFRAS) of the
fishing units and labourers, emergence of multiday fishing
maritime States of India. The main emphasis of MFRAS is
even extending beyond 15 days and consequent
on regulating fishing vessels in the 12-nautical mile
socioeconomic disturbances. In this context, there is good
territorial sea, mainly to protect the interests of fishermen
scope to increase our food fish production through open
on board traditional fishing vessels. Thus, the Act has been
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
mainly used for the purpose of maintaining law and order
legislation so far enacted by the central Government and
at sea. The MFRAS were first implemented in the States
various state Governments focussed mainly to regulate
of Kerala and Goa in 1980. They were subsequently
the harvesting of open sea resources rather than
enacted in other States, the latest being in 2003, in
considering the farming in the sea.
Gujarat. While the earliest MFRAS were enacted only for
At present (2003-04) there are 2251 traditional landing
regulation of fishing vessels along the coastline of the
centres, 33 minor and 6 major fishing harbours in the
State, the Gujarat MFRA provides for protection,
marine fisheries sector of India. About 1.77 lakh of fishing
conservation and development of fisheries in inland and
crafts are in operation comprising 76596 traditional non-
territorial waters of the State of Gujarat and for regulation
mechanised fishing crafts, 50922 motorized crafts and
of fishing in the inland and territorial waters along the
49070 mechanized crafts operating different gears as
coastline of the State. The Coastal Regulation Zone
shown in Table 1.
Protection Act, (1986) outlines a zoning scheme to
Table 1 Growth rate of marine fishing fleets in India (1961-62 to 2003-04)
Year
1961-62
1973-77
1980-81
1997-98
2003-04
SECTOR
Non-mechanised
Number
Growth Rate
(%)
Motorised
Number
Growth
Rate (%)
Mechanised
Number
Growth
Rate (%)
Number
90424
106480
137000
160000
76596
—
—
—
32000
50922
—
8086
19013
47000
49070
90424
—
156013
239000
176588
—
18
29
17
-52
—
—
—
—
59
—
—
135
147
4
Total
Growth
Rate (%)
—
—
73
53
-26
regulate development in a defined coastal strip. The
The trends in the growth rate of fishing units indicate the
Notification defines the coastal stretches of seas, bays,
possible phasing out of non-mechanised Canoes at least
estuaries, creeks, rivers and backwaters which are
in certain regions, which ultimately reflected a negative
influenced by tidal action in the landward side, up to 500
growth of 52 per cent by them during 1997-98 to 2003-
m from the high-tide line (HTL) and the land between the
04. This downtrend is compensated in the motorised
low-tide line (LTL) and the HTL, as the CRZ. The
sector implying large-scale motorisation of existing
Environment Protection Act, (2002) authorizes the
traditional crafts. Mechanised crafts displayed a major
Central government to protect and improve
boom during 1980s and 1990s. The growth rates were
environmental quality, control and reduce pollution from
135 and 147 per cents respectively in 1980 and 1997, due
all sources, and prohibit or restrict the setting and/or
to diversification and extended area of operation. While
operation of any industrial facility on environmental
mechanized trawlers and gillnetters are common all over
grounds. The Biological Diversity Act (2002) provides for
Indian coast, dolnetters are popular in Gujarat and
the conservation of biological diversity, the sustainable
Maharashtra coasts, purseseines in Goa, and Karnataka
use of its components and, significantly, the fair and
coasts, pair trawling in Tamil Nadu and sona boats in
equitable sharing of the benefits arising out of the use of
Orissa coasts, depending on the regional and seasonal
biological resources, knowledge and related matters. Open
abundance of resources. When the technical efficiency
sea mariculture requires adequate legislative support from
of a particular gear is better than the other, the lesser
the Government for leasing out of suitable sites. The
efficient gears gradually disappear from the operation.
107
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
The gross capital investment on fishing units in Indian
most of the non-mechanised fishermen are having one
marine fisheries sector during 2003-04 works out at Rs.
or two fishing nets, which are not sufficient for efficient
10,532crore in which mechanised sector constitutes about
operation for the whole year.
Rs. 9,049 crore, more than a three-fold increase from
1997-98. The increase in investment on mechanised
trawlers and gill-netters are comparatively higher than
other sectors. The capital investment on motorised sector
also almost doubled from Rs.456 crore during 1996-97
to Rs. 861 crore during 2003-04. However, as expected,
the non-motorised sector has shown a decline in
investment from Rs. 923 crore during 1996-97 to Rs. 622
crore during 2003-04 in tune with their decline in
production and diminishing returns. Further, substantial
numbers of these units were converted into motorised
units.
In the open access marine fisheries, mode of ownership
on means of production by fisherfolk greatly influences
the occupational pattern and socio-economic status. The
type and number of fishing implements owned is the
yardstick to measure the economic well being of a fisher
household. In India, hardly 13 per cent of the active
fishermen in the marine fisheries sector have ownership
on craft and gear in 2003 and another 3 per cent possess
only gears. The proportion of owner operators in marine
fisheries declined over the years with the increasing capital
requirement for possessing motorized and mechanized
fishing units. In the mechanised sector 12 per cent,
The estimated gross capital investment on fishing
motorised sector 9 per cent and traditional sector 21 per
equipments alone works out to Rs. 4,117 crore at 1997
cent have ownership on crafts and gears. Most of the
price level , in which 58 per cent is in the small scale
non-motorised units are operating as family enterprises
mechanized sector, 9 per cent in deep-sea vessels, 11 per
not even realizing the operating cost of the labourers.
cent in motorized sector and 22 per cent in non-
Lack of finance and credit facilities does not allow these
mechanized sector. It may be noted that out of the total
fishermen to go for modernization and come out of the
capital investments on fishing equipments, during 2003,
vicious circle of poverty and low-income trap. Disguised
86 per cent is constituted by mechanised sector, 8 and 6
unemployment is rampant in capture fisheries and
per cents respectively by motorised and non-mechanised
fisherman need alternative avocations for their livelihood.
sectors.
The inter and intra sectoral migration also need to be
The overall per capita investments of an active fisherman
in 2003-04 was Rs.86,290 ranging from Rs.17,024 in the
non-mechanised sector to Rs. 2,19,319 in the mechanised
sector. During 1997, the overall per capita investment was
Rs. 40, 363, where the investment per head in mechanised
arrested for balanced and sustainable development of the
coastal sector. Fishermen are in general unwilling to shift
from fisheries sector for any other employment. Hence,
mariculture is one of the most acceptable and viable
occupations for coastal fisher folk.
sector was Rs.1, 25,689, motorised and non-mechanised
A report of the consultative group on international
sectors invested Rs. 26, 835 and Rs. 13,979 respectively
agricultural research states that within the next 15 years,
per active fisherman in India. Further, fishing intensity is
fish farming and sea ranching could provide nearly 40 per
directly related with capital investment vis-à-vis number
cent of all fish for the human diet and more than half of
and type of nets they are possessing. A catamaran owner
the value of the global fish catches. According to a report
having different types of nets can have more number of
of the FAO, the world aquaculture production is projected
fishing days. If he is having only one type of net, he will
to increase by 2.69 times by 2025 AD. India as a leading
be having only lesser number of fishing days. In India,
country in Asia in aquaculture production should be able
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Central Marine Fisheries Research Institute
From 14 - 23 December 2009
to achieve at least a production of 2mt (0.1mt finfish,
The concept of Responsible Fisheries advocated by FAO
1.0mt crustaceans, 0.3mt molluscs and 0.6mt seaweeds)
through its Code of Conduct for Responsible Fisheries is
through mariculture by the year 2025 AD, i.e., 3.9 per
an epitome among global efforts for realising the coveted
cent of projected global aquaculture production of 51.8mt.
goal of sustainable utilization of our marine resources.
With improvements in the domestic market,
The Code is a landmark in marine development thinking
diversification of marine products exports, availability of
as it represents the consensus achieved by more than
a vast range of cultivable candidate species, several
150 nations across the world on the directions we should
culture technologies and hydro climatic (or agro climatic)
follow in order to avoid resource depletion due to irrational
zones for coastal mariculture and sea-farming, India is
utilisation behaviour pattern shown by various
poised to become one of the world’s leading producers of
stakeholders. Stock enhancement through artificial reefs
mariculture products.
and fish farming in the cages are better technological
Issues related to Coastal Regulation Zone (CRZ),
Integrated Coastal Zone Management (ICZM) and the
options to counter problems of resource depletion.
Scope for open sea mariculture
unfounded apprehensions that coastal mariculture would
adversely affect the environment, are leading to
Prospects of Open sea mariculture
unnecessary or avoidable litigations retarding the growth
z
Alternative source of income
of the mariculture sector. It is worth to note that the
z
Better resource productivity
z
Entrepreneurship development
z
Societal empowerment lower and
z
Lower gestation period.
present shrimp oriented, land-based coastal mariculture
has resulted in the under-utilisation of the technologies
developed for the culture of bivalves, seaweeds and pearls,
and hence, requires being diversified and broad-based to
take maximum advantage from the high production
potential of tropical aquaculture farms.
Problems of cage culture
The information from various segments reveals that the
z
Lack of coherence among social groups
z
Issue of free rides among the commons
versatile study on responsible fisheries observes that the
z
Problem of mute participation
major factor that endangers its sustainable utilization is
z
lack of social commitment
z
Problems in revenue sharing system
unanimously agreeable regulatory mechanisms. There are
z
Resource ownership issues
many activities, which adversely affects the sustainability
z
Need for finding progressive fisher folk
z
Risk taker and innovator
z
Entrepreneurship development
marine fisheries in India is currently undergoing through
a phase of socio-economic cum ecological turbulence. A
the open access nature of marine resources and the
veritable lack of an enforceable property rights regime or
of marine resources including shallow water mining, use
of improper crafts, ghost fishing, destruction of mangrove
forests, etc. Development processes such as urbanisation,
industrial pollution and eutrophication of estuaries have
also jeopardised the fragile ecological dynamics of the
coastal area.
The following interventions are required for promotion of
cage culture
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1) Cages
Participatory approaches for cage culture
z
Increasing the life of the cage
z
Sharing of accountability and responsibility
z
Cost reduction of the cage
z
Security for group conflicts and sabotage
z
Optimization of cage and mooring system
z
Institutional support in the event of uncertainties
z
Provision of subsidies for the cage construction
z
Reward for risk bearing
z
Encouraging a public private community participatory
2) Site selection and candidate species
z
Identification of congenial site considering the
hydrographic and environmental parameters
z
Identifying location specific candidate species with
better productivity inputs are required
3) Inputs
approach
There is enormous scope to enhance food fish production
from the sea through mariculture. Adaptability of capital
intensive fishing technologies in the capture fisheries will
further escalate the cost of production and price of fish.
Unlike land, water resource is not a limited factor of
z
Input standardization
production for coastal states for adopting mariculture
z
Cost minimization
practices. Hence, legislative support is vital for the
z
Revenue sharing approach
promotion and propagation of open sea mariculture. It
provides better option for enhancing the livelihood
The other interventions are increasing density and revenue
opportunities of the fisherfolk in the coastal sector
sharing approach.
without any migration.
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Geographic information systems and site
selection issues of open sea cage culture
J. Jayasankar
Central Marine Fisheries Research Institute, Post Box no. 1603
Ernakulam North P.O., Kochi - 682 018, Kerala
jjsankar@gmail.com
The GIS paradigm
the core of earth are reasons for their pattern, the external
As is much known in the Information Technology circles,
environment like the atmospheric parameters and other
a pair of numbers narrates the past, describe the present
natural habitation like forests etc have a very important
and in fact most importantly seal the future. The pair
role in moderating their availability. Hence the idea of
obviously means the latitude and longitude of the location
viewing the geographic location as another latent cause
any where under the sky. This perspective of referencing
of expression of any important parameter alongside
any type of information be it scientific, sociological,
temporal references started clawing up on the ladders of
psephological or economic, has taken the world of
analysts and a whole new vista of analytical reasoning
analytics by storm in past quarter of a century. The last
emerged. That vista loosely named as analysis of geo-
decades of the previous millennium were dotted with
referenced series or spatial analytics has a very important
spurt in methodologies and software which were totally
requirement, a series of spatially referenced data spread
dependent on this type of geo-referenced data.
across temporal spectrum. The series of spatio- temporally
Information collected serially over time, popularly known
arranged data points are popularly referred to as
as time series, always had a huge role to play in studying
Geographic Information System or GIS in short. When
the impact of changing eras and centuries at larger level
originated the GIS concept was mostly applied to
and seasons and cycles in shorter duration. The
terrestrial references. The absoluteness with which the
surreptitious shadow cast by the effect woven by time
terrestrial data points could be uniquely referred by a pair
on the trait of interest had always caught the imagination
of geographic coordinates amply suited the development
of analytical computational experts, especially
of databases which were strongly rooted on those
econometricians. Similar to the perpetual latent impact
coordinates. Hence a plethora of application-ware were
of temporal causes, the geographic factors also have been
developed which led to the possibility of developing maps
exhibiting impact on many an important scientific
on the digitised geographic platform showing various
phenomenon. Most of the natural resources available on
intensities with which the parameters of interest were
earth are bound to be impacted by their geographic
available. These maps are popularly referred to as
position on the earth’s crust. This is best explained by
“Thematic Maps” and they formed an essential part of
the availability of resources like ores and mines in certain
many a dossier on resource spread, intensity and
pockets on earth. Though geological reasons arising from
availability. But GIS is much more than development of
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thematic maps. The range of applications is multifaceted
nucleus of marine GIS technology. It is quite constructive
including geo statistics, modelling and development of
to have stress on the importance of meta data while
decision support systems.
detailing the basic types of data on the very first occasion.
Although terrestrial GIS has been quite in vogue in the
The goal of marine GIS has always to be kept in mind
past quarter century or so, the last decade saw the
before trying to understanding the technical intricacies.
emergence of another dimension to it, literally. The Marine
Ranging from exploratory input to full fledged predictive
Geographic Information System (MGIS) has the added
paradigms, the MGIS has a huge chunk of goals which
dimension of depth alongside the latitude and longitude.
could be attained using specially drafted software. The
It has been a much discussed and researched topic that
core concepts of MGIS starting from location up to
the marine fauna and flora demonstrate huge
diffusion have strong relationship with various types of
diversification down the bathymetric locales. Marine GIS
information collected at various stages of the resource
must first adapt to the characteristics of the marine world
regeneration system. One standout example that could
and marine data and the dynamic relations among the
be cited is the association of regions using chlorophyll
various components of the marine environment. Thus
contents and sea surface temperature. Another way of
MGIS opens up a new world of opportunity as well as
looking at this whole paradigm is to pose self quizzing
challenge which is 3 dimensional to say the least.
queries and seeking answers like, “Where was it”; “How
At this juncture the importance and utility value of 3D
marine data sets as compared to the lat- long based
terrestrial datasets have to be clearly understood. The
depth component, needless to add, holds the key towards
unravelling a huge treasure of wealth and its dynamics
across the geographic vastness as well as their vertical
upheaval. Such a three coordinate time series can always
aid in shoring up the onerous task of studying the
underlying interrelationships, trend, seasonality etc.,
which classically suit spatio-temporal analyses. Such a
system can mutually embellish species life history data
which in turn can aid in lucid portrayal of the progression
down the prey- predator web. The interlinked nature of
coastal, oceanic and fisheries information is for everybody
to understand and study. The invaluable contribution that
such a marine GIS can make while attending to the
conflict between marine object dynamics and
management policies is anybody’s guess. Another topic
worthy of discussion is the type of input getting into a
marine GIS including those obtained by meteorological
gadgets as well as by Global Position Systems. A variety
of technical disciplines and issues are associated with the
long was it existing?”; “Is there any other resource
abundant nearby?” etc. A model which satisfactorily
answers the above asked questions would be the one
which would be the best.
MGIS and Oceanography
GIS in general and MGIS in particular are affronted by
Oceanographic concepts in many ways. The extent of
influence can be well understood by the simultaneous
consideration of micro scale turbulence to enormous
gyres, both of whom have a serious role to play in shaping
up the Information System. The role of Remote Sensing
in these oceanographic data consideration has also been
a topic of discussion and debate. Needless to say a
management interface for coastal and oceanic
environment is a much needed reality for any nation caring
for justifiable exploitation of its resources. No better
argument is needed for this aspect of exposition than the
fact that 90% of pollutants generated by economic
activities end up in coastal zone. It is a matter to ponder
that the historic reasoning behind oceanic upheavals and
their vulnerability to climate change which is a present
day priority, have been comprehensively juxtaposed. The
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inevitability of viewing the coastal zone from the
artificial reefs which are bound to add strength and
stakeholder’s point of view in the holistic perspective
objectivity to the more publicized perception on GIS.
rather than a fractured sector by sector basis can never
Popular techniques like ecological modelling, scenario
be under stated.
building and vulnerability index computation on a geo
Innumerable citations and references are available for the
linking of oceanographic parameters with a MGIS Starting
with datasets vis-à-vis their relevance to marine geology
to information based accrued over hydrological sounding
and multi-beam sonar systems, the review could be
referenced platform have also been some of the much
highlighted applications of MGIS. The MGIS is also a widely
used tool to study and manage lesser focussed marine
contingents like submerged aquatic vegetation, wetlands
and watersheds.
elaborate and informative Please refer V. Valavanis (2002)
Literature is replete with initiatives taken by various
for an excellent review.
governmental and research establishments towards
The role of GIS in flood assessment is another important
facet full of references on digital elevation models,
geographic flood information system and the world map
of natural hazards. The citations available in Valavanis
(2002) sufficiently sum up the efficacy and range of the
tool.
Oceanographic GIS. The developments in the Gulf, US and
Europe have been worth chronicling (Valavanis (2002)).
But the flagging of GIS as a solution to the ever increasing
data volume and complexity should be approached with
caution, as prima facie the statement indicates data
redundancy and Information Systems target something
primarily different. The issue of handling voluminous
An exposition on the application of GIS in coastal and
datasets usually target solutions in the mould of data
oceanic management throws up interesting works like
warehousing and Information Systems should not be
Natural Resources Management Facility for Mozambique,
equated with them.
which primarily aim at social development like
employment generation and poverty alleviation through
participatory and sustainable management of natural
resources. Certain attempts to rank coastal regions on
their environmental sensitivity and pollution hazard with
the help of GIS have also been discussed in literature.
Throwing spotlight on yet another facet of GIS, work done
by researchers across the globe by integrating
hydrodynamics and morphometry are worth revisiting
(Valavanis (2002)). The analytics done in describing a
dynamic coastal zone like a lagoon ecosystems along with
identification of main aspects of their degradation and
identification of critical environmental parameters as also
recovery plan will really spur the researcher towards
seeking more on this application of GIS.
In all there are around 20 unique efforts carried out at
various locations across the globe till the turn of the last
millennium Valavanis (2002). Most of the information
systems mentioned are of very high environmental
importance and their role in arriving t multidisciplinary
answers to important scientific and societal queries can
never be understated.
Any logical extension of global examples of MGIS would
be the focus on data sampling methods which broadly
outlines the gadgetry involved in the collection of physical,
chemical and biological data that add up to make the
system. The point that commercial establishments have
fanned out their research and analytical wings across the
globe to sustain their interests through Oceanographic
trend monitoring, is probably one single stand out fact. It
There are multitudes of references on GIS application for
effectively sums of the impetus being thrust on this
study of oil spills in oceans, sea level rise and natural and
branch of study and the enormity of changes and paradigm
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shifts which are just round the corner. The information
folk. Unlike hydrology and other physicochemical
on various satellite sensors and the corresponding internet
parameters, fish capture and availability based indicators
sources are real highs which have augmented the reach
have a very huge say on the holistic management of
and purpose of MGIS. The development of other sources
fisheries encompassing social, economic, technical,
of remote sensed data like sensing platforms, Ocean Data
ecological and ethical aspects. Any information system
Acquisition System etc. is a meticulous collation on
that has roots on this type of core information will have a
advances in Oceanographic data sampling. Plethoras of
whole lot of relevance and priority amidst its class of
urls in the internet have comprehensive information
systems. Naturally more criticisms and evaluations are
regarding the details of the gadgets.
bound to tow them. The Net is replete with references
wherein umpteen instances of applications based on MGIS
Another interesting issue discussed during the course of
coming to the aid of fisherfolk and planners in various
this topic is the one pertaining to real-time organisation
countries. Interestingly another interesting aspect of the
of marine survey data. Though it may sound similar to
link between Information Systems and Fisheries is the
the type of data integrations discussed so far to an
role of geostatistics (spatial statistics) which is an
innocuous reader, this throws up more light into the
established branch of statistics inquiry into the geo
integrated analytics that follow the online data
referenced datasets. Albeit tools like kriging and
accumulation. Hardware innovations like tape robot is
variograms have been in vogue in the GIS universe they
undoubtedly a fascinating interlude to this, but it has the
are basically statistical tools which are adopted or adapted
capability to derail a serious analytical researcher by
to suit to the requirements of geo referenced datasets.
leading him into the fascinating world of clustered data
storage management.
A large number of techno-administrative information
consortia formed across the world catering to the fisheries
This discussion could be rounded of with a detailed
GIS (Valavanis (2002)). The chronological developments
exposition on the methods and techniques adopted in
that have taken place in the electronic documentation
identification and quantification of gyres, classification
and documentation of strides made by this branch of IT
of surface waters, identification of temperature and
are worth browsing through. The first GIS conference at
chlorophyll fronts and tracking and measurement of
Seattle in 1999 is a proof for this. While reiterating the
upwelling. The mode of discussion is a judicious admixture
intricacies involved in the comprehensive understanding
of generic introduction followed by specific examples of
of the relationship of fish and its environment, the
the techniques application across the globe. The
conference stressed that it is time to have a syndicated
description of the unified efforts involved in the mapping
effort to publish scholastic efforts in this direction. The
of sea beds where local and remote methods of data
statement – “The time has arrived for a Fisheries GIS
derivation come to the fore cited in Valavanis (2002),
could aptly wrap up the extensive discussion on GIS and
its application in Oceanography.
MGIS and Fisheries
MGIS with a firm footing on various sources of information
journal…” made by the participants (although it was made
in early 2000’s) sums up the sincerity with which this
document is prepared. Although the trickles which were
chronicled in many publications have turned into a stream
nowadays, an exclusive periodic publication of articles
on GIS for marine fisheries is still elusive.
is obviously well poised to have many applications in the
The four stages at which GIS on fisheries can be utilised
fisheries sector which have direct impact on the fisher
are worth underscoring. Most of the planning and policy
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compilers get saturated with the thematic maps and
salmon fisheries were developed (Valavanis (2002)). The
conceptual 3D output generated by GIS software. The
discussion includes inclusion of environmental variables
other stages viz. which area meets the set requirements,
alongside the classical parameters like expanse of water
presence or absence of a pattern over space and scenarios
bodies etc. which gives a ringside view of initiatives made
which can arise as a result of decisions and regulations
in the first part of this decade.
are weightier in purpose but less in vogue when it comes
to utilisation. Hence it is mandatory for any discussion
on adoption of GIS to equally stress all the four levels of
the tool’s application. One important aspect to be
highlighted on marine fisheries management through GIS
is a citation of Senegalese case (Valavanis (2002)) which
can be quite useful in the context of any similar footed
nation. GIS was utilised to identify areas of conflict
between artisanal and industrial fisheries and further
proceeding on to the explanations for fisheries
management on the degree of respect for the limits of
regulated fishing areas and spatial fishing strategies as
per the major seasons. The development of bioenergetic
physiological principles augmented generalised spatial
dynamic age structured multistock production model is a
refreshingly new vista of GIS application in fisheries
research. As another application of GIS in marine fisheries
management, the mapping of biomes, large marine
ecosystems etc. which go a long way in evaluating and
explaining the distribution of marine features (e.g. primary
production), which are not usually focussed upon under
conventional studies can be mentioned. In a way there is
an exhaustive collection of references which unravels all
the possible utility areas of GIS in marine fisheries
management (Valavanis (2002)).
The use of remote sensing tools in the applied portion of
data collation is another aspect of study. The grid
construction and partial ground truthing of the remote
recordings are all inseparable parts of this methodology
and they can always be adequately described with the
help of certain specific studies whose outputs like maps
etc. have been provided (Valavanis (2002)). A list of more
than 60 Internet sources of GIS databases embellishes
the chapter and it has been one of the unique plus points
of this book as such. A couple of snapshots from some
GIS databases which include very pertinent theme maps
like gear pressure on cephalopod populations in SE
Mediterranean and catch areas of Octopus in the same
area are excellent techniques to communicate with the
starter Valavanis (2002). Developments like mapping of
spawning grounds, essential habitats, migration corridors
etc. which give a taste of how powerful and useful GIS
can be in a fishery planner’s hand.
MGIS and cage culture
Open sea cage culture being an operation wrought with a
lot uncertainties ranging from physical parameters of the
ocean to the biotic and chemical factors affecting the
morbidity and mortality rates of the animals to be cultured
has to be necessarily based on informed plan. An informed
The role of GIS in aquaculture needs no further emphasis
plan is one where studied decisions are taken before the
as it is almost similar to the terrestrial GIS wherein primary
blue print is prepared which in turn are based on various
role is in site selection. Herein come the issues of planning,
parameters of concerned recorded pertaining to the area
designing and execution of aquaculture assignments,
of operation. Hence when the ocean can pose challenges
apart from simulation backed economic forecasting tools,
at least on three dimensions with a whole lot of physical
which is a real plus for observers with less exposure.
and chemical parameters on the tow. It is here the role of
During the turn of last century some working models to
manage and study thriving inland fisheries like freshwater
a geo- spatial aggregation of parameters comes to
prominence.
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Site selection for cage culturing exercises will involve
specific inputs on the following parameters:
(i)
Bathymetry
(ii) Currents
(iii) Shelter and
(iv) Water Quality Variations
To explain this with an example to have a cage culture
study based on Salmonids, it is essential to gather
information on depth (m), current (m s-1), dissolved
oxygen (mg l-1), salinity (%) and temperature (æ%C). From
The drogues could be located at timed intervals from boats
using sighing compasses.
established literature inputs on the possible range and
The fourth parameter of exposure could be categorised
optimum values of these parameters might have to be
by estimating wave heights at different locations.
collected. Such data coupled with topography of the site
Expected wave heights depend upon water depth and
and exposure of the same would be used in the site
wind velocity, duration of fetch over which wind passes
assessment.
before impacting the proposed location.
Towards achieving this preliminary studies conducted in
The wind data could be obtained from nearby weather
the area focussed have to be collated and compiled. Then
stations.
suitable software to store/ update and analyse the data
may have to be selected. This software could range from
free to very cheap shareware to software meant for
educational/ research institutions to full fledged
commercial software like Arc GIS etc. As the next step
the topography of the broader location where cage is
The physico-chemical properties of the water like
dissolved oxygen, temperature and salinity could be
recorded at a number of fixed locations at different stages
of tidal cycle using instruments like Oxygen meter and
inductive bridge salinometer.
planned to be set up along with the nearby coast details
The whole database in GIS pertaining to the area under
like bay etc should have to be mapped. The outline map
focus should preferably be prepared in two scales which
of the greater area like bay could well be a definitive
are significantly different in resolution, something like 25
starting point. Suitably scaled maps have to be drawn
x 25 metre block or 10 x 10 m block based.
outlining the broader area of focus.
In any typical GIS software the different types of
The second task is to generate a bathymetric contour map
information like outline map, points of observation,
of the broader area of interest which could be achieved
bathymetric data, current and exposure data are entered
by making a series of boat transects at constant velocity
in the form of different layers called grids. Usually the
and bearing using echo-sounders. Depths such recorded
base grid containing the blocks is kept transparent and
could be plotted onto the base map.
the other observed data sets are over laid on them either
The third task of measuring the velocity of currents is
as points or shapes or themes.
done by using hydrographic drogues (sea anchors)
Apart from these specific information that needs to be
(displayed below).
known for the type and size of cages, general information
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of the broader area like pollution, availability of power
For proceeding further the following are the parameters
(electricity) and presence or absence of tourist-related
estimated during the exercise.
or ecological limitations.
In the following series of pictures provided in the paper
by Ross et al (1993) graphically explains the details of
one such GIS mapping done to locate suitable ambience
for Salmoid cages.
(i)
Mean depth : 6.8 m
(ii) Current velocity : Upto 138 cm s-1
(iii) Speeds falling in acceptable range : 80%
(iv) Nature of velocities: High at periphery; low near
centre
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(v) Spatial interpolation: CURRINT
over dependence of the precision of parameters estimated
(vi) Dissolved Oxygen levels: 8.6 to 11.0 ppm (at high
makes it overtly vulnerable to instrument/ equipment
tide) ; 8.2 to 10.4 ppm (at low tide) (no difference
errors. But one huge plus for this approach is the avoiding
between surface and bottom readings)
of individual bias and subjectivity while zeroing in on the
(vii) Water temperature: 12.8C to 13,4 C and 12.9C to
13.0 C at high and low tide respectively. (well within
the tolerance level)
(viii) Salinity parameter: 19% to 29%
location of choice. Still unfavourable locations can be
removed at the outset by way of observing cage depth
and limiting beyond 1.5 times of the depth. Such dictums
like avoiding velocities less than 5 cm s-1 and those above
50 cm s-1 should be built keeping in mind the species to
(ix) Wind speeds: 61 km h-1 and 85 km h-1
be cultivated. The sequences to be followed in the
(x) Fetches observed 4.44 (NW), 3.42(NE) and 2.37 (NE)
decision making process should be ceremoniously
were the longest
followed for any interchange of layers may produce
(xi) Wave heights: 0.4 to 0.8 m
different output.
Based on the type of data collected over a reasonable
With the advent of brutal computational power the
period of time scorecard was prepared for the site
process of decision making especially the computations
selection. The scores with not more than two to three
involved are of no big threat. But an assiduous selection
outputs were decided based on the various parameters
of decisive parameters and careful measurement of
discussed above and the highest score is given to the
parameters during survey is a must for any successful use
blocks which have the most favourable parametric value.
of MGIS technique for selecting Cage locations for
Finally to decide on the suitable block (25 x 25 m) or (10
x 10m) the interpolated wave heights coupled with
bathymetry will decide the score on the depth aspect.
Similar recoding based on the scores for other parameters
like water quality was conducted and the most ideal
pocket was selected based on the pocket/ block which
scored the maximum. (SUITABLE in the picture shown
above).
While this method seems to be straight forward and
deeply rooted in the classical analytical traditions, the
mariculture.
References
(i)Slater (1982). Learning through Geography , pp 340, Heineman
Educational Books, Ltd, London
(ii)Valavanis, V. (2002) Geographic Information Systems in
Oceanography and Fisheries, London: Taylor and Francis,
2002, 209pp., USD $80, £45.00, hb (ISBN 0-415-284635).
(iii) Ross, L.G, Mendoza, E.A and Beveridge, M.C.M (1993) The
application of geographical information systems to site
selection for coastal aquaculture: an example based on
salmonid cage culture: Aquaulture. 112 pp 165- 178
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Economic analysis of cage culture of sea bass
Narayanakumar, R.
Central Marine Fisheries Research Institute, Post Box No. 1603
Ernakulam North P.O., Kochi- 682 018, Kerala, India
ramani65@gmail.com
Introduction
return per rupee invested is the economic indicator that
Open sea cage farming can be referred to as the method
guides the investor to choose a particular enterprise or
of culturing aquatic organisms in enclosed cages made of
practice. Besides, the analysis of the economic
various materials in the seas. The true cage farming is of
performance serves as an indicator for the investor to
recent origin and a well established practice in Southeast
allocate his resources in the enterprises. This becomes
Asian countries. The practice developed independently in
very much essential, since the resources are scarce and
a number of countries, all in Southeast Asia. Presently,
the investor is interested to invest his scarce capital
cage culture is developing fast and turning to a highly
resource in that enterprise that gives the maximum return
commercialized business activity in many Asian countries.
for his investment.
In India, pen culture and pond culture experiments were done
The economic performance of the cage culture experiment
along the southeast coast using the seed of rabbit fish,
is worked out by calculating the annual fixed costs,
groupers and sand whiting. Similar trials were also done along
variable costs and the annual total costs from the cost
Kerala and Karnataka coasts. In the recent years, open sea
side. From the returns point of view, the harvest from
farming was done at Visakhapatanam and cage/pen culture
the cage, the gross revenue from the sales of the harvest
experiments were conducted at Calicut and Vizhinjam
is worked out. Using the cost and returns figures, the
Research Centre of CMFRI (CMFRI Annual Report, 2006, 07).
following economic indicators are estimated to test the
economic viability and financial feasibility of any
During 2008, fourteen cages were launched across the
enterprise.
east and west coasts. The failure witnessed in the launch
of the first cage during May 2007, formed the stepping
Table 1 Indicators of economic performance of the cage
stone of success later in the same place. The lacunae in
culture enterprise
the launching of the first cage were rectified and
Sl.No.
Economic Indicators
successfully re-launched during December 2007, which
1
Initial investment of the cage
gave a substantial harvest of sea bass in April 2008.
2
Fixed cost (For crop duration of six months)a)
Depreciation b) Insurance (2% on investment)c)
Interest on Fixed capital (12%)d) Administrative
expenses
The success of the adoption of any innovation or new
3
Total Annual Fixed cost (A)
technology lies in its economic performance. The rate of
4
Operating costsa) Cost of seedlingsb) Cost of feeding and
other labour chargesc) Interest on working capital (6%)
Economic analysis
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5
Total Operating or Variable cost (B)
6
Total cost of production [Row(3)+Row(5)]
7
Yield of sea bass (in kg)
8
Gross revenue [(7) * Price per kg]
9
Net income [(8)-(7)]
10
Net operating income [(8)-(5)]
11
Cost of production (Rs./kg)[ (6)/(7)]
The detailed economic analysis of the experimental cage
12
Price realized (Rs./kg) (8)/(7)
culture practice demonstrated in Visakhapatnam (Andhra
13
Capital Productivity (Operating ratio) (5)/(8)
Pradesh) and Balasore is given below to indicate how the
assess their performance in Table 1. This will serve as the
guidelines to the institutional agencies who are extending
the financial support to the enterprise.
Case studies
The different economic indicators of the economic
performance of cage culture enterprise are worked to
economic analysis of the enterprise is done.
(A) Visakhapatnam
Table 2 Initial investment of the cage culture farm of 1061 m3
Sl. No.
Items
Investment (in Rs.)
% to total
Economic life (in years)
1
HDPE Cage frame
4,00,000
27.12
10
2
HDPE nets
3,00,000
20.34
10
3
Galvanized Iron Chains
80,000
5.42
10
4
Mooring equipments
60,000
4.07
10
5
Stone Anchors
1,50,000
10.17
50
6
Floats
1,50,000
10.17
10
7
Shock absorbers
25,000
1.69
10
8
Ballast
35,000
2.37
10
10
9
Ropes-HDPE
10
One time launching charges
Total Initial Investment
35,000
2.37
2,40,000
16.27
14,75,000
100.00
Table 3 Details of Annual Fixed cost
Sl. No.
Details
1
Depreciation
2
Insurance premium (5% of investment)
3
Interest on fixed capital
4
Administrative expenses (2%)
Amount (in Rs.)
1,16,000
73,750
1,77,000
29,500
Total fixed cost
3,96,250
Table 4 Details of Annual Variable cost of cage culture (for a crop duration of seven months)
Sl. No.
Details
Cost
% to total
1
Feeding
2,24,000
14.02
2
Seedling
1,50,000
9.39
3
Feed cost
9,00,000
56.32
4
Net cleaning
75,000
4.69
5
Underwater inspection
50,000
3.13
1.56
6
Net mending and Maintenance
25,000
7
Post crop overhauling
20,000
1.25
8
Security
1,00,000
6.26
9
Interest on working capital @6% for one crop duration
Total
54,040
3.38
15,98,040
100.00
121
National Fisheries Development Board
National Training on 'Cage Culture of Seabass' held at CMFRI, Kochi
Table 5 Economic indicators of the cage culture of Lates calcarifer
Sl.No.
Details
1
2
3
4
5
6
7
8
Annual fixed cost
Annual Variable cost
Annual total cost
Gross revenue (after harvesting from 5th to 7th month)
Net operating income
Net income (profit)
Capital Productivity (Operating Ratio)
Annual Rate of return to capital
Amount (in Rs.)
3,96,250
15,98,040
19,94,290
37,50,000
21,51,960
17.55,710
0.43
119%
(B) Balasore
economic parameters indicate that this open sea cage
At Balasore, the initial investment for a 6m diameter cage
farming of sea bass is economically viable.
worked out to Rs.3,00,000. The fixed costs for the culture
Conclusion
period of six months was calculated at Rs.54,000. The
Thus it is seen from the above results that the economic
variable costs of the culture operation worked out to Rs.
analysis of the experimental cage culture farm has worked
2,31,750. Thus the total cost of production to the
out successfully with higher net operating income and net
participants worked out to Rs.2,85,750 (Table 6).
income in a crop period of seven to nine months. It is to be
Table 6 Economic analysis of the experimental cage culture demonstration at Balasore
Sl. No.
Details of cost and returns
1
2
Initial investment for a 6m diameter cage
Fixed cost (For crop duration of six months)a)Depreciation b)Insurance
(2% on investment)c) Interest on Fixed capital (12%)d) Administrative expenses
Total Fixed cost (A)
Operating costsa) Cost of seedlingsb) Cost of feeding and other labour chargesc)
Interest on working capital (6%)
Total Operating cost (B)
Total cost of production (Six months)
Yield of sea bass (in kg)
Gross revenue from 3032 kg
Net income (8)-(5)
Net operating income (Income over operating cost)
Cost of production (Rs./kg) (6)/(7)
Price realized (Rs./kg) (8)/(7)
Capital Productivity (Operating ratio) (5)/(8)
3
4
5
6
7
8
9
10
11
12
13
Amount (in Rs.)
3,00,000
30,0003,00018,0003,000
54,000
50,0001, 75,0006, 750
2,31,750
2,85,750
3,032
5,75,760
2,90,010
3,44,010
94.24
189.89
0.50
The culture of sea bass yielded 3.03 tonnes of sea bass
noted that once the practice is further expanded to many
during the harvest conducted at the end of six months,
areas and farms, the cost will decline due to the economies
thus earning a gross revenue of Rs. 5,75,760 to the
of scale of operation. Thus it could be concluded that the
participants. The culture of sea bass earned a net
open sea cage farming is a viable alternative and
operating income of Rs. 3,44,010 at the end of six months
economically & financially feasible mariculture operation
and a net profit of Rs.2,90,010 at the end of the same
for the stake holders to make use of. The State Fisheries
period. The cost of production per kg of sea bass worked
Departments and the Development Organizations like
out to Rs.94.24 against the value realization of
NFDB can promote the concept of cage culture on a large
Rs.189.89per kg. The capital productivity measured
scale with their institutional and financial support availing
through operating ratio worked out to 0.80. These
the technical expertise developed at CMFRI.
122
Central Marine Fisheries Research Institute