Distinctive Characters: Dorsal fin with 3 spines and 23-24 rays. Anal fin with 20-21 rays. Pectoral fin with 13-15 rays. No grooves infront of eyes. 4-5 rows of small forward curving spines posteriorly on body. Caudal fin rounded, the corners acute.
Colour: Ground colour olive brown above, pale below. Black band across body, and black triangular patch on caudal peduncle. Black areas partially outlined with green-yellow. Orange at base of pectoral.
Habitat and Biology: Common in the shallow outer reef environments exposed to surge. Diet even more varied than R. aculeatus, feeding on a wide range of invertebrates, fishes and also algae.
Remarks: Rhinecanthus rectangulus is readily distinguished from R. aculeatus (previous page), on the basis of colour pattern. Both are found in shallow areas, but R. rectangulus prefers more exposed locations. R. rectangulus is a very wary fish, hence difficult to approach under water.