Yellow-striped cardinalfish

Appearance

''O. cyanosoma'' is usually a blueish silver color with orange-yellow stripes, and grows to be an average of 6 centimeters. It lives in waters up to 50m in depth, often in lagoons or coral reefs. It is active during the nighttime, feeding on small plants and animals, mostly plankton.

Large examples of ''Ostorhinchus cyanosoma'' grow to 8 cm in length although its average length is 6 cm. The fish is colored silver with a blueish tinge, and has six orange-yellow stripes including a short stripe behind the eye.

A new species was separated out in 1998 from the ''O. cyanosoma'' species complex, with almost identical morphology but with a pinkish-red spot on the tail base, and the genetics were confirmed in 2014. Notably, whilst Bleeker noted red fins in his original sample, he never noted a red tail spot.

Naming

No one has described a synonymous species, so Bleeker's original species name ''cyanosoma'' remains unchallenged. However, the genus ''Apogon'' which he placed it in masked significant differences between species. More recently, on the basis of physical and genetic characteristics, it has been transferred into the genus ''Ostorhinchus''.

On the journey to dissecting the ''O. cyanosoma'' species complex now incorporating ''O. cyanosoma'', ''O. rubrimacula'', ''O. wassinki'', and ''O. properuptus'', the last was for a while considered a synonym of ''O. cyanosoma''.

Reproduction

''O. cyanosoma'' is a paternal mouthbrooder. This is likely to be a more important reason for the sexual dimorphism shown by the male's wider gape and more protruding lower jaw, than is its prey specificity. A bigger mouth allows for more eggs to be protected from predation, and for better water circulation .

Pair bonding in ''O. cyanosoma'' does not appear to provide the expected genetic benefits of monogamy, indeed like many pair bonding fishes in its family, predation seems to have driven it rather than reproductive exclusivity.

Food

''O. cyanosoma'' is mainly a nocturnal planktivore, emerging from hiding in coral caves and crevices to feed by hovering just above sandy microhabitats on coral reef flats. By defecating during the daytime in a non-feeding microhabitat, ''O. cyanosoma'' probably helps cycle reef nutrients around different communities on the reef. It appears to prefer to eat small benthic sergestid crustaceans rather than the planktonic larvae to be found higher in the water column. However, seasonal or sampling effects may play a role in defining the diet, since in certain years, certain sites appear to suggest that ''O. cyanosoma'' is actually eating significant amounts of planktonic copepods and crustacean larvae.

Interestingly, although its wide mouth gape may be well suited to eating benthic prey, consumption of varying types of prey by cardinalfishes with different mouth shapes appears in reality to be better correlated with varying availability .

Cultural

It has been the subject of research to test what might happen to marine life by the year 2100, due to predicted carbon dioxide levels in the atmosphere.