Orangespine Unicornfish

Max length : 46.0 cm SL male/unsexed

Found in areas of coral, rock, or rubble of lagoon and seaward reefs. Benthopelagic. Adults usually in small groups. Juveniles in shallow rocky reefs, sometimes in small aggregations mixed with other acanthurids of similar size. Feed mainly on leafy brown algae (Sargassum and Dictyota). Sometimes in large aggregations. Very seldom poisonous. Pair-spawning has been observed. Most are algae eaters and keep the reef from getting clogged with coral-smothering algae. While edible, they tend to taste a bit like the seaweed they diet on.  They are also called surgeon fish due to the sharp, extensible knife-like spines on their tail. 

Dorsal spines (total): 6; Dorsal soft rays (total): 28-31; Anal spines: 2; Anal soft rays: 29 - 31. Dorsal fin black, the black continuing as a pointed projection onto nape, with a pale blue line at base and a broad outer white zone on soft portion; anal fin mainly orange; dorsal and anal fins with a narrow blue margin and black submarginal line; caudal fin with a yellow submarginal band posteriorly. Caudal fin emarginate with adult males having trailing filaments from each corner

Summary of Distribution: Pacific Ocean: Honshu, Japan south to the Great Barrier Reef and New Caledonia and east to the Hawaiian Islands, French Polynesia, and Pitcairn. Eastern Pacific: Clipperton Island. Once regarded a wide-ranging Indo-Pacific species, the Indian Ocean population is now recognized as a separate species, Naso elegans.
Note: Distribution range colors indicate degree of suitability of habitat which can be interpreted as probabilities of occurrence (fishbase.org)