The Banggai cardinalfish (Pterapogon kauderni) is a small tropical cardinalfish in the family Apogonidae. It is the only member of its genus. This attractive fish is popular in the aquarium trade. It is among the relatively few marine fish to have been bred regularly in captivity, but significant numbers are still captured in the wild and it is now an endangered species. The detrimental impact of humans on its environment and certain fatal diseases threaten this species' numbers significantly. Iridovirus diseases are known to be significant reason for fish mortality.
This species grows up to 8 centimetres (3 in) total length. It is easily differentiated from all other cardinalfishes by its tasseled first dorsal fin, elongated anal and second dorsal fin rays, deeply forked caudal fin, and color pattern consisting of three black bars across the head and body and prominent black anterior edges on the anal and second dorsal fin. The male can be differentiated from the female by a conspicuous, enlarged oral cavity, which is apparent only when they are brooding.
This species is restricted to the Banggai Islands of Indonesia. This species has an extremely limited geographic range (5,500 km2) and small total population size (estimated at 2.4 million). The Banggai cardinalfish is composed of isolated populations concentrated around the shallows of 17 large and 10 small islands within the Banggai Archipelago. A small population also occurs off Central Sulawesi, within Luwuk harbor. One additional population has become established in the Lembeh Strait (North Sulawesi), 400 km north of the natural area of the species distribution, following introduction by aquarium fish traders in 2000. Small populations seen (May 2014) in Secret Bay, north west Bali (Banggai cardinal fish, Secret Bay, Bali)
The Banggai cardinalfish is the only member of its family that is diurnal. It is a demersal tropical marine fish that forms stable groups of about 9 individuals in shallow water, being most common at 1.5 to 2.5 m in depth. It inhabits a variety of shallow habitats, including coral reefs, seagrass beds, and open areas of sand and rubble. It is most common in calm habitats on the protected side of larger islands. It is often found associated with the seagrass Enhalus acoroides and the long spined sea urchin Diadema setosum. It occurs among various living benthic substrates such as sea urchins, sea anemones, and branching corals; young fish are most commonly associated with sea anemones, while juveniles and adults occur most frequently among long-spined sea urchins and branching corals, as well as sea stars, hydrozoans, and mangrove prop roots. Individuals of 2 to 60 hover above the urchins, with the younger ones about 2 to 3 centimeters SL staying closest to them. The fish retreat among the spines when threatened. Individual fish exhibit well-defined homing behaviour and return to the original location of their group when disturbed. The Banggai cardinalfish often coexists with various anemonefish and anemone shrimp when sheltering in anemones and corals; when found among sea urchin spines, it associates with several other genera of cardinalfish. Following removal of the fish by aquarium collectors, the abundance of associated invertebrates has been shown to decline.
This fish is an opportunistic feeder. Its diet includes planktonic, demersal, and benthic organisms. Copepods constitute the bulk of its diet. It serves as an important food source for several species of lionfish (Pterois spp.), the honeycomb grouper (Epinephelus merra), the crocodilefish (Cymbacephalus beauforti), the snowflake moray (Echidna nebulosa), the estuarine stonefish (Synanceia horrida), and the yellow-lipped sea krait (Laticauda colubrina).
The Banggai cardinalfish is a paternal mouthbrooder. The female plays an active role in courtship and pair formation, which occurs a few hours to a few days before spawning. Mating pairs establish spawning territories several meters away from the main group and vigorously defend them. The eggs are about 2.5 mm in diameter. The young remain in the male's mouth cavity for an undetermined period after hatching. Unlike many other species of marine fish, the Banggai cardinalfish lacks a planktonic stage in its life history. The species has a short lifespan, reaching around 4 years in optimal conditions in captivity, and perhaps 1 to 2 years in the wild.
Banggai cardinalfish are sexually monomorphic. The pairs form up to 2 weeks prior to spawning. The female courts the male from pair formation until spawning. The female's size determines the fecundity and egg size, but the male's size determines the reproductive output, or the number of the eggs that the pair produces. Therefore, pairing tends to occur among individuals of similar sizes, so the male is able to care for all the eggs that the female produces.
In Banggai cardinalfish, courtship behavior is usually initiated by the female. Upon choosing a mate, the female isolates her potential mate from other individuals in the colony by creating a spherical spawning site that is about 50–60 cm in diameter. The general movement that the female exhibits is called‘side by side trembling' which is when the female approaches the male from behind with a vigorous trembling motion while the male stays motionless. Then she places herself alongside him and tilts her body thirty degrees outward from its vertical plane, when the male and female's caudal and anal fins come into contact. The female repeats this movement until the male responds with sporadic 'mouth opening,’ a sign of receptiveness. Such courtship behavior may last from several hours to 2–33 days. When an intruder interrupts a female's courtship behavior, the female would rapidly and aggressively chase the intruder away if the intruder is of the same sex. However, when the secondary male, or the intruder male approaches, he, instead of the female, exhibits trembling behavior, and also helps to defend the female and primary male's isolated territory. If the primary male does not respond to female's trembling, the female leaves periodically to visit the secondary male and displays trembling behavior which often results in mating.
The Banggai cardinalfish is a popular aquarium fish among fishkeepers.
The fish is collected by local fishers and sold into the aquarium trade. This species first appeared in the international trade around 1995 or 1996. By 2001, 600,000 to 700,000 fish were exported annually. Trade estimates for 2001 through 2004 are 700,000 to 900,000 fish per year with collection occurring throughout the archipelago. Surveys identified significant (>90%) declines in two populations that were fished from 2001 to 2004, including the extinction of a population off of Limbo Island.
This fish has been successfully bred in captivity. Captive breeding presents an alternative to wild-caught fish. Initially, the relatively high cost–benefit ratio of its production combined with the large number of less expensive wild-harvested fish prevented expansion of aquaculture efforts. In recent years, prices for captive bred or aquacultured specimens have plummeted as large numbers have entered the market. As of early 2018 aquacultured individuals are regularly available for as little as $14 U.S. per fish, and aquacultured specimens make up the vast majority of the market. In addition, a newly emerging threat in the form of a viral disease has been documented in wild-harvested individuals maintained in captivity.
Collection for the aquarium trade has threatened this species with extinction. This increases the demand for captive-bred specimens. It is listed as an endangered species by the IUCN based on its small range, the fragmentation of its distribution, and its continuing decline due to exploitation for the international aquarium trade. In 2007, the species was proposed to be listed for protection under CITES Appendix II, which could limit export of wild-caught individuals, but Indonesia would not support this, and the proposal was withdrawn.
