A plain blue-grey unicornfish with no horn, feeding on plankton in mid-water off Red Sea drop-offs.
To 75 cm fork length, commonly 50, which makes it the largest surgeonfish on this site. It has no horn: the head profile is smooth and slightly rounded. The body is elongate and streamlined, much more torpedo-shaped than the disc-shaped surgeonfish, dark brownish-grey shading to yellowish underneath, often with a pale area around the mouth and a dark-edged gill opening. There are bony plates on the base of the tail that become keels with age. It can change colour quickly, sometimes going pale blue-grey when feeding or at a cleaning station.
The grey unicornfish is genuinely difficult to separate and the two are often reported together. This one has a more yellowish belly and less strongly keeled tail plates. The unicornfish that grow horns are no trouble.
It is a plankton feeder, not an algae grazer, which is unusual for the family and explains where you meet it: large schools hanging in blue water off a drop-off in daylight, taking crab larvae, arrow worms and pelagic tunicates. It lives between the surface and 150 m and is usually deeper than 10 m. The tail keels are fixed and cut; the risk is from handling.
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.