Surgeonfishes (family Acanthuridae) are strikingly colored and patterned reef fishes. They are daytime grazers that travel in large schools, constantly moving as they snap up bits of algae. Some species have a moveable scalpel-like spine (used for defense) that folds forward into a groove on either side of the base of the tail, accounting for both the scientific and common names for the family.

The Yellowfin Surgeonfish (Acanthurus xanthopterus) is a large surgeonfish (up to around 60 cm) with a distinctive yellow blotch behind and in front of the eye, pectoral fins with yellow on at least the outer third, a bluish tail (often with a whitish band at the base), dorsal and anal fins with 4 to 5 dull yellow stripes alternating with blue (the base with a pale blue band), and a black spine sheath. The caudal (tail) spine is relatively small. Adults usually occur in small to large groups and are found especially around deep offshore reefs, generally below around 20 m down to a maximum depth of about 90 m. Juveniles live in shallow protected areas. Yellowfin Surgeonfishes graze the surface of sand and rubble for soft algae. These common fish are found throughout the Indo-Pacific and tropical eastern Pacific south to KwaZulu-Natal (eastern coast of South Africa).

(Randall et al. 1997; Smith 1997; King anfd Fraser 2002)