Convict surgeonfish (Acanthurus triostegus) is a small surgeonfish in family Acanthuridae of the order Perciformes. It is typically about 10 cm (3.9 in) long, but some individuals may grow larger than 20 cm. Dorsal spines (total): 9; Dorsal soft rays (total): 22-26; Anal spines: 3; Anal soft rays: 19 - 22. Body olivaceous gray, with 4 vertical stripes (1 stripe on head across the yellow eye; 1 on caudal peduncle); shading to white ventrally, often with a sharp line of demarcation. Sharp, forward-pointing, erectile spine on each side of caudal peduncle which folds down into a groove. Scales minute. Teeth with denticulations on sides and top. Gill rakers 18-22 in anterior row, 19-24 in posterior row.
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Distributed in indo-Pacific and Eastern Pacific. Adults occur in lagoon and seaward reefs with hard substrate; young abundant in tide pools.
Benthopelagic. Often feeding near where certain algae grow on rocks that are grazed. Occasionally form schools; feed on filamentous algae in large aggregations.
During spawning, clouds of eggs and sperm are preyed upon by eagle rays which are often present during spawning. Form spawning aggregations.
Utilized as a food fish.
The sexes are separate among the acanthurids (Reeson 1983). Acanthurids do not display obvious sexual dimorphism, males assume courtship colours (J.H. Choat pers. comm. 2010). This species spawns year-round in equatorial waters, but seasonally in Hawaii, coinciding with the colder part of the year (February-March) (Randall 1961b). It recruits year-round in Guam (J. McIlwain unpub. data).