The adult and the juvenile look like different fish, and for a long time they were.
Adults are unmistakable: a deep body to about 40 cm ruled with twenty-odd blue and yellow horizontal bands, a black mask through the eye edged in electric blue, and a dark bar across the gill cover ending in a yellow tail. Juveniles are entirely different — black with concentric white and blue rings, the outer ones closing into an oval at the rear. The change runs through an untidy intermediate stage at around 8 to 12 cm in which the rings break up and the first horizontal lines appear. Juveniles were described as a separate species in the nineteenth century, which is why older books carry both names.
Adults patrol a large home range along a slope, feeding on sponges and tunicates, and usually keep moving. Juveniles do the opposite: they hold to a single crevice, often under a coral head or in a wreck, and circle back to it. That makes the juvenile the easier photograph, though the space is dark and tight. A cruising adult will generally allow a diver to parallel it at three or four metres but turns away from a direct approach, so waiting on its line of travel works better than following. Recorded from about 3 to 50 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.