Light blue-grey to dark olive-brown, narrow dark vertical stripes.
Horn becomes longer with age.
Size : 60 cm
Habitat : In deep lagoons and at outer reef slopes, 1-50 m. Usually in groups in the open water where it feeds on plankton. Juveniles and sub-adults graze on algae growth.
Can abruptly change colouration, e.g. during the mating ritual the male displays a broad, pale-blue crossband at the front of its body.
Distribution : Red Sea to South Africa, SW Japan, Hawaii and Ducie Islands.