Distinctive Characters: Dorsal fin with 9 spines and 23 rays. Anal fin with 3 spines and 20 rays. Pectoral fin with 2 spines and 13 rays. A compressed body with a small mouth. First dorsal spine short, about one third of second dorsal spine. First anal spine short. Pectoral fin shorter than head. A lancet-like spine on caudal peduncle, which folds into a deep horizontal groove.
Colour: Greenish grey dorsally, shading to white below, with six narrow black bars on head and body.
Habitat and Biology: An abundant inshore reef species which feeds on filamentous algae. Often seen in large feeding schools; young common in tidepools.
Distribution: Indo-Pacific and Eastern Pacific.
Remarks: Acanthurus triostegus is a very common species in the Maldives. This species is of little interest among aquarists.