Order Perciformes Family Acanthuridae (Surgeonfishes, tangs, unicornfishes) Thompson's surgeonfish Acanthurus thompsoni(Fowler, 1923). 27.0 cm TL Dorsal spines (total): 9; Dorsal soft rays (total): 23-26; Anal spines: 3; Anal soft rays: 23 - 26.
Distribution; Indo-Pacific/East Africa, including the Mascarene Islands to the Hawaiian, Marquesan, and Ducie islands, north to southern Japan, south to Rapa(Austral Islands). General; Body uniformly blue-gray to dark brown, almost black. Caudal fin pale in color(snow white in live fishes). Small, dark spot below and adjacent to axil of pectoral fin. There is a single black spot on the posterior end of second dorsal fin base above the peduncle. With crescent-shape tail, its tail fin is bright white. however, In Hawaiian waters its tail fin is dark, the same color as the body. Might two species be involved? Other than color, there seem to be no physical differences between the two. Perhaps the issue could be resolved by DNA. If there are two species, the Hawaiian one will retain the name thompsoni because it was originally described and named from Hawai`i in 1923 ("type locality"). It will be considered endemic. Its cousins outside the Islands will probably be called Acanthurus philippinus, a name given in 1927 to white-tailed specimens obtained in the Philippines. At present, A. philippinus is considered a "junior synonym" of A. thompsoni.
Anterior gill rakers 15-18; posterior 14-16. Snout length 7.9 to 8.2 times in SL. Least depth of caudal peduncle 2.2 to 2.5 times in head length. This occasionally schooling species occurs in steep outer reef slopes and drop-offs. Occurs in either singly or in small groups, and occasionally in aggregations of hundreds. Feeds on zooplankton, well above the bottom, or away from the wall in drop-offs, particularly large gelatinous forms, and on fish eggs and crustaceans. It is generally seen in less than 30 m and may occur in as little as 4 m. Depth range 4 - 119m. No evidence of sexual dimorphism.
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