UnicornfishesNasinae

Unicornfishes are large surgeonfishes, with an elongated, laterally compressed body and a small, terminal mouth. All species bear two fixed, bladed spines on each side of the caudal peduncle, used for defence. While body colouration is typically shades of grey, olive, or brown, it can rapidly change in response to surroundings or behaviour. Several species develop a prominent horn-like protuberance or a distinct hump on the forehead, giving the group its common name. These fish grow up to 70 cm (2.3 ft) in length.

They inhabit exposed reef slopes, drop-offs, and outer reef channels, observed between 5 and 100 metres (16-330 ft) depth. Unicornfishes primarily graze on benthic macroalgae; some species also feed on zooplankton in the water column. Adults are often found singly or in pairs, though juveniles and subadults may form small schools, and large aggregations can occur.