The butterflyfish are one of the most colorful inhabitants of coral reefs. The name is suggestive of their behavior, flitting about shallow to deep reefs to search for food. They travel singly or in pairs and lose their deep color and markings when they become inactive during the night.
Butterflyfish (Chaetodontidae, pronounced key-toe-DON-ti-day) are one of the most delightful groups of fish observed by snorkelers. There are 114 family members worldwide; only six inhabit our region. Four species are prominent, conspicuous members of reef communities. Their small size (less than six inches), rounded bodies and slightly concave foreheads easily distinguish them from angelfish, which are larger, have rounded foreheads and generally exhibit elongated dorsal and anal fins.
Reminiscent of their butterfly namesake, these small, colorful fish spend their days flitting about shallow to deep reefs, dock pilings and rubble fields using keen eyesight to search for tiny worms and other invertebrates. Butterflies generally travel singly or in pairs within a rather limited range. At dusk they find shelter in a reef recess and become inactive. As they settle in for the night, their daytime colors pale and markings change.
Life is much simpler for fishwatchers when a fish’s distinctive feature (a marking or anatomical feature that distinguishes it from a similar appearing species) is part of its common name. Fortunately, this is the case for all four butterflies described in this article. Let’s take a look at Banded Butterflyfish first. Their two dark midbody bands make them a snap to identify by simply associating the bands with the species’ name. Note the dark band running through the eye; at first, this might seem a distinctive feature until you notice that similar markings are present in all four species. Eye bands, believed to be a survival adaptation of several fish species, help camouflage the location of their true eyes. This characteristic confuses potential predators as to the direction the little fish will dart when attacked.
Foureye Butterflyfish are also easy to recognize and recall. Their distinctive feature is the black spot, ringed in white, on the rear body. This characteristic, known as a false eyespot, is thought to further befuddle predators as to correct location of the true eye. If you count the two real eyes and the two false eyespots, you quickly come up with the species’ name, Foureye Butterflyfish.
Identification of Spotfin Butterflyfish is a bit trickier. Again, their common name is the fishes’ distinctive feature – a small, black dot on the outer margin of the rear dorsal fin. These are the only family members with a dot on any fin and also the only species with all yellow fins. However, if you try to remember the fin color as the distinctive feature it will be of no help associating it with the Spotfin’s name.
Longsnout Butterflyfish break the traditional family mold by varying somewhat from their relatives in size, shape, habitat and behavior. Longsnouts average only two to three inches in length, have longer, even more pointed snouts, generally inhabit deeper reefs and walls, are more wary of divers and are almost always solitary. To some, the Longsnouts’ high dorsal fin resembles a new wave hairdo. Of course, their distinctive snouts make their name a cinch to remember.
Juvenile butterflyfish are not only smaller than adults but they also display distinctly different markings. It is thought that these clear differentiations limit territorial aggression from their elders while the little fellows grow. Juveniles tend to live near protective niches in shallow patch reefs and seagrass beds. They are occasionally sighted hovering close to the openings of discarded conch shells. The pictured juvenile Foureye has an extra set of ocellated spots and pale bands; these markings disappear as the fish matures.
During your next reef snorkel see how many butterflyfish species you can identify.