Butterfly Fish

             The butterflyfishes are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera. A number of species pairs occur in the Indian and Pacific Oceans, members of the huge genus Chaetodon.
Butterflyfishes look like smaller versions of angelfish (Pomacanthidae), but unlike these, lack preopercle spines at the gill covers. Some members of the genus Heniochus resemble the Moorish idol (Zanclus cornutus) of the monotypic Zanclidae. Among the paraphyletic Perciformes, the former are probably not too distantly related to butterflyfish, whereas the Zanclidae seem far less close.

Description and Ecology

              Butterflyfishes mostly range from 12 to 22 cm (4.7 to 8.7 in) in length. The largest species, the lined butterflyfish and the saddle butterflyfish, C. ephippium, grow to 30 cm (12 in). The common name references the brightly coloured and strikingly patterned bodies of many species, bearing shades of black, white, blue, red, orange and yellow. Other species are dull in colour. Many have eyespots on their flanks and dark bands across their eyes, not unlike the patterns seen on butterfly wings. Their deep, laterally narrow bodies are easily noticed through the profusion of reef life. The conspicuous coloration of butterflyfishes may be intended for interspecies communication. Butterflyfish have uninterrupted dorsal fins with tail fins that may be rounded or truncated, but are never forked.
             Generally diurnal and frequenting waters of less than 18 m (59 ft) (though some species descend to 180 metres (590 ft)), butterflyfishes stick to particular home ranges. The corallivores are especially territorial, forming mated pairs and staking claim to a specific coral head. Contrastingly, the zooplankton feeders form large conspecific groups. By night, butterflyfish hide in reef crevices and exhibit markedly different coloration.
Their coloration also makes them popular aquarium fish. However, most species feed on coral polyps and sea anemones. Balancing the relative populations of prey and predator is complex, leading hobby aquarists to focus on the few generalists and specialist zooplankton feeders.