Butterflyfish (Chaetodontidae) are a family of striking, tropical, perch-like marine fish. They are found on the coral reefs of the Atlantic, Indian and Pacific Oceans. They are quite small, usually between 12 and 22 centimeters. The largest species, Chaetodon lineolatus, can reach 30 centimeters. There are about 127 species, grouped in 11 genera. The territorial species are often aggressive towards their peers. Adult specimens often mate for life.
Some species feed on coral polyps, others on zooplankton. The first species in particular is strongly territorial, claiming, often in pairs, their own pieces of coral as their territory.
The nickname butterflyfish has to do with the bright bright colors and color shades such as black, white, blue, red, yellow and orange. This makes them also popular among aquarists. One problem is that many species feed on coral polyps and these are difficult to grow in tanks. Many species have a patch behind the eyes and black bands over the eyes, much like the wings of butterflies. The colors probably mainly have a signaling function towards other species. Their tall and flat bodies make them suitable for hunting for food in narrow rock crevices. They have continuous dorsal fins, with the caudal fin being either round or rectangular, but never v-shaped.
The family name Chaetodontidae is derived from the Greek words chaite meaning hair and odous meaning tooth. This mainly refers to the bristle-shaped teeth in their narrow pointed mouth. Butterflyfish resemble the angelfish of the family Pomacanthidae but can be distinguished by the lack of the sharp backward-facing spine behind the gill slit.
Butterflyfish lay many floating eggs that mix with the plankton and are carried downstream.
Not all butterflyfish can equally successfully be kept in an aquarium. Robbert Fenner has given a list of species in Het Aquarium of July/August 1998. “The ones that can be kept well generally stay alive and the ones that can’t be kept well die easily”