Fish and Coral Information
The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group.
The butterflyfish 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 Indian and Pacific ocean, members of the huge genus Chaetodon, and their taxonomy has often been confused by whether these should be considered species or subspecies. Recent work using DNA sequence data has resolved many of these questions. Also, numerous subgenera have been proposed for splitting out of Chaetodon, and it is becoming clear how the genus ought to be subdivided if that is desired.
Butterflyfish 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
Butterflyfish are fairly small, mostly from 12 to 22 cm (7-9 in) in length. The largest species, the lined butterflyfish and the saddle butterflyfish, C. ephippium, grow to 30 cm. The common name references the brightly coloured and strikingly patterned bodies of many, bearing shades of black, white, blue, red, orange and yellow. Some species are dull in colour however. Many have eyespots on their flanks and dark bands across their eyes, not unlike the patterns seen on butterfly wings. Their deep, laterally compressed bodies are easily noticed through the profusion of reef life, leading most to believe the conspicuous coloration of butterflyfish is 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 shallow waters of less than 18 m (though some species descend to 180 m), butterflyfish stick to particular home ranges. The corallivores are especially territorial, forming mated pairs and staking claim to their own head of coral. Contrastingly, the zooplankton feeders will form large conspecific groups. By night butterflyfish hide amongst the crevices of the reef and exhibit markedly different coloration than they do by day.
Their coloration also makes butterflyfish popular aquarium fish. However, most species feed on coral polyps and sea anemones. This poses a problem in most reef tanks where a delicate balance is to be maintained. Species kept in the hobby are therefore the few generalists and specialist zooplankton feeders.
Butterflyfish are pelagic spawners; that is, they release many buoyant eggs into the water which then become part of the plankton, floating with the currents until hatching. The fry go through what is known as a tholichthys stage, wherein the body of the postlarval fish is covered in large bony plates extending from the head. They lose their bony plates as they mature. uch a curious armoured stage is seen in only one other family of fish, the scats (Scatophagidae).
Taxonomy, systematics and evolution
The family name derives from the Ancient Greek words chaite ("hair") and odontos ("tooth"). This is an allusion to the rows of brush-like teeth found in their small, protrusile mouths.
The Chaetodontidae can be divided into two lineages that might arguably be considered subfamilies. But this is not usually done, and the subfamily name Chaetodontinae has fallen out of use as it was a leftover from the times when the Pomacanthidae and Chaetodontidae were united under the latter name as a single family. Hence, Chaetodontinae is today considered a junior synonym of Chaetodontidae. In any case, one lineage of Chaetodontidae (in the modern sense) contains the "typical" butterflyfishes around Chaetodon, while the other unites the bannerfish and coralfish genera. As the "Perciformes" are highly paraphyletic, the precise relationships of the Chaetodontidae as a whole are badly resolved.
The fossil record of this group is marginal. This is mainly due to the fact that they are restricted to coral reefs where animal carcasses are liable to be dispersed by scavengers, overgrown by corals, and even if they fossilize it is likely that sooner or later erosion will destroy them. However, there is Pygaeus, a very basal fossil from the mid-late Eocene of Europe, dating approximately from the Bartonian 40-37 million years ago (mya). Thus, the Chaetodontidae emerged probably in the early-mid Eocene. A crude molecular clock in combination with the evidence given by Pygaeus allows to place the initial split between the two main lineages to the mid-late Eocene, and together with the few other fossils it allows to deduce that most living genera were probably distinct by the end of the Paleogene 23 mya.