The white-and-black pennant fish, and the one most often mistaken for a Moorish idol.
A white fish to about 25 cm with two broad black bars, yellow dorsal and tail, and the fourth dorsal spine drawn out into a long white pennant that can reach beyond the tail on an adult. It is routinely confused with the Moorish idol, which has a longer, more tapered snout, a third dark band across the tail region, and no forked tail. The schooling bannerfish Heniochus diphreutes is the closer look-alike: it has a rounder snout, a shorter pennant, and forms mid-water aggregations of dozens, while acuminatus is usually in pairs.
Pairs hold a stretch of slope and feed on plankton and small benthic invertebrates; juveniles sometimes clean parasites from larger fish. They are among the least shy of the reef butterflyfishes and will often approach a stationary diver. Recorded from a few metres to about 45 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.