Schooling Bannerfish

The schooling bannerfish belongs to the Chaetodontidae, the butterflyfish family. Its strongly compressed body carries two broad black diagonal bands on a white ground, while the tail and the rear of the dorsal fin turn bright yellow. The fourth dorsal ray extends into a long white filament that streams above the fish and earns it the name false moorish idol. It reaches 21 cm. It resembles the longfin bannerfish (Heniochus acuminatus) so closely that the two are routinely confused in shops; diphreutes is told apart by its rounder breast and less protruding snout. The species ranges across the Indo-Pacific, from the Red Sea and East Africa to Hawaii and Polynesia, including cooler subtropical waters. It is usually seen between 5 and 30 metres along outer reef slopes and in current-swept channels, though it descends far deeper in places. Unlike its cousin it lives in schools, sometimes large ones, hanging in open water above the reef and picking zooplankton from the current. Juveniles, and occasionally adults, act as cleaner fish. In the aquarium it is among the easiest butterflyfishes to feed: a committed planktivore, it quickly takes mysis, brine shrimp and frozen preparations offered several times a day. It does demand volume, 600 litres minimum, and a long open swimming lane, since it patrols the water column constantly. Keep three or more, introduced together, as fish added separately tend to squabble. Peaceful towards tankmates, it is considered reef-safe provided it is generously fed; underfed specimens will nip soft corals and LPS. Captive breeding remains exceptional.