Family Chaetodontidae
butterflyfishes

Chaetodontidae, or butterflyfishes, are among the most widely recognized coral reef fishes. Their vivid coloration and striking patterns make them popular in the aquarium trade, although some species are difficult to maintain in aquaria (see Economic Importance). The family contains 10 genera with 114 species, the majority in the genus Chaetodon. They occur mainly in tropical waters, most densely distributed in the Indo-West Pacific, but some occupy warm temperate waters (see Habitat). Members of this family vary considerably in terms of color, but all butterflyfishes share certain morphological traits such as a deep, laterally compressed body, ctenoid scales that extend onto the soft-rayed portions of the dorsal and anal fins, and jaws that may be slightly or extremely elongated (see Physical Description). Jaw shape and size correlates with the type of prey consumed; some butterflyfishes feed upon small invertebrates or algae, others solely on coral polyps (known as obligate corallivores), and still others upon zooplankton (see Food Habits). Butterflyfish are largely pair-forming, pelagic (in the water column) spawners (see Reproduction), and are unique among reef fishes in that the larvae pass through a stage termed tholychthys during which a bony sheath encases the head (see Development). As of 1994, five chaetodontid species were listed as vulnerable to extinction (see Conservation Status). (Bellwood and Wainwright, 2002; Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002; Kuiter, 1993; Moyle and Cech, 2000; Nelson, 1994; The World Conservation Union, 2002; Thresher, 1984)

Butterflyfishes are primarily tropical, although some species can be found in temperate regions. Most species occur in the Indo- West Pacific, from Australia to Taiwan. Only four species occur in the eastern Pacific, and 13 species in the Atlantic. (Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002; Kuiter, 1993; Nelson, 1994)

Butterflyfishes are a marine family occupying tropical to warm temperate waters. Some occur in the brackish water of estuaries and protected bays, commonly along steep parts of rocky reefs. They are most often found in shallow (less than 20 m) water near coral reefs, but some are deepwater dwellers descending to 200 m. Some occur in seagrass habitats, deep mudflats, or shallow lagoons. Juveniles of many species occupy different areas than adults, such as tidal pools, boulder reefs and shallow areas without coral. Some investigators hypothesize that butterflyfishes may have originally been pelagic, non-reef fishes that colonized coral reefs on two or more separate occasions. (Bellwood and Wainwright, 2002; Kuiter, 1993; Nelson, 1994; Thresher, 1984)

The Chaetodontidae (butterflyfishes) family is made up of 10 genera with 114 species. The genus Chaetodon contains 89 of these species, distributed among 13 subgenera. Butterflyfishes formerly were placed in one family with angelfishes , but have since been separated on the basis of numerous morphological differences. Butterflyfishes are part of an unranked group named the Squammipinnes, so called for the scales that cover the soft-rayed portions of the dorsal and anal fins. (Helfman, Collete, and Facey, 1997; Nelson, 1994)

Butterflyfishes are brightly-colored, often yellow or white, with darker contrasting markings that may conceal the eye. They, like some other reef fishes, are sometimes described as “poster-colored” due to their vivid coloration. They typically have a false eye spot near the back of the body, which may be an anti-predator adaptation (see Predation). These fishes are laterally compressed (very thin when viewed from the front) but deep-bodied, appearing almost circular from the side. Strongly sheathed dorsal, pelvic, and anal fin spines accentuate the disk-like body shape. The continuous or slightly notched dorsal fin contains six to 16 spines and 15 to 30 soft rays. The caudal fin is rounded and has 15 branched rays. The body is covered with small ctenoid scales that extend well onto the dorsal and anal fins. Butterflyfishes have small mouths filled with brushlike, close-set teeth. Their snouts are pointed, with the degree of elongation depending on the species and the type of food it consumes. Some, such as Forcipiger flavissimus, have extremely long jaws like tweezers that can grasp invertebrates from narrow crevices. Others, such as Chaetodon ornatissimus, have short jaws for nipping off live coral polyps. The jaws of some butterflyfishes can measure more than 25% of their body length. Butterflyfishes are, in general, sexually monomorphic (males and females look alike), although occasionally males have been found to be larger than females. Depending on the species, butterflyfishes range from nine to 30 cm in length. (Click here to see a fish diagram). (Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002; Kuiter, 1993; Moyle and Cech, 2000; Nelson, 1994; Thresher, 1984)

Butterflyfish eggs are spherical, buoyant, and transparent, and, for those species observed, hatch in 28 to 30 hours. A drop of oil behind the yolk suspends the newly-hatched fish upside down just beneath the surface. By the time an individual reaches 5.5 mm, it enters the tholichthys larval stage, unique among reef fishes, in which bony armor covers the head. The sheath of thin bony plates extends beyond the head to form spines dorsally and ventrally. The shape and form of the plates and spines varies from species to species, but in general tholichthys larvae are silver-colored, deep bodied, and laterally compressed. These pelagic larvae may be planktonic for two or more months. The bony plates are absorbed within a few weeks after the fish settle to the bottom. The larvae settle at night and transform quickly into juveniles. In many species of butterflyfish, juveniles have a color pattern that is quite distinct from their adult form. Butterflyfishes most likely reach sexual maturity when they are about a year old. (Johnson and Gill, 2002; Kuiter, 1993; Thresher, 1984)

No specific information was found on butterflyfish longevity, but it can be surmised that most species live at least three years and probably longer, since they reach sexual maturity after about a year and many pairs are reported to be stable for at least three years. (Thresher, 1984)

Butterflyfishes are usually seen in stable heterosexual pairs, although some species move in schools or foraging groups. Sometimes a single species will school in one geographic region, and only occur in pairs elsewhere. Juveniles are typically solitary, and some act as cleaner fishes. Butterflyfishes are active during the day and move conspicuously around the reef. (Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002; Kuiter, 1993; Moyle and Cech, 2000; Thresher, 1984)

Daytime feeders, butterflyfishes use vision to find their prey. Pairs also communicate visually; if a pair becomes separated, one may swim upwards in a display that helps the two locate each other. During agonistic encounters between members of Chaetodon lunula, the fishes’ yellow colors intensify and their countershading fades, a visual signal of aggressive interaction. (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2000)

Generally benthic feeders, many butterflyfishes eat small invertebrates, sponges or polychaete worms. Some feed on zooplankton, and others exist exclusively on coral polyps. Another feeding method is scraping the surface of live coral to obtain algae, attached invertebrates, and mucus from the coral. Some are herbivores, grazing on the filamentous algae covering coral reefs, and a few eat seagrasses and algae on reef flats. Butterflyfishes have long snouts, with the degree of elongation depending on the species and the type of food it consumes. Some, such as Forcipiger flavissimus, have extremely long jaws like tweezers that can grasp invertebrates from narrow crevices. Others, such as Chaetodon ornatissimus, have short jaws for nipping off live coral polyps. The jaws of some butterflyfishes can measure more than 25% of their body length. (Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002; Kuiter, 1993; Moyle and Cech, 2000; Nelson, 1994; Thresher, 1984)

Most butterflyfishes have a dark band obscuring the eye, and often have a false eye spot in contrasting colors near the tail. These two attributes may confuse predators. The ocelli, or eye spots, may reduce damage from fin-biting predators by mimicking the head. Another possibility is that the ocelli are a signal to help maintain cohesion in shoaling groups. (Helfman, Collete, and Facey, 1997; Johnson and Gill, 2002)

Butterflyfishes, like many other reef fishes, have coevolved with other organisms in their environment. Benthic invertebrates on the reef have developed heavy armor, spines, toxins, and adherence to the substrate, and butterflyfishes have evolved a variety of jaw forms that allow them to penetrate narrow crevices, reach exposed parts of invertebrates, or nip off coral polyps. The herbivorous members of the family have an impact as well, for their grazing of algae is important for the well-being of the reef. They, and other herbivorous reef fishes, keep algae that might otherwise smother the coral cropped to a mat one to two mm thick. (Moyle and Cech, 2000)

No specific information was found concerning any negative impacts to humans.

Butterflyfishes are one of the most popular tropical fishes with divers and aquarists. Some do well in aquaria but those that eat only coral are almost impossible to keep successfully. (Kuiter, 1993; Thresher, 1984)

As of 1994 there were five species of butterflyfish listed as vulnerable to extinction, all in the genus Chaetodon. Their vulnerability is based on the limited spaces in which they are found, making them extremely susceptible to human activities in those areas. (The World Conservation Union, 2002)