Acanthurus blochii Valenciennes, 1835
Ringtail surgeonfish
photo by Randall, J.E.

Family:  Acanthuridae (Surgeonfishes, tangs, unicornfishes), subfamily: Acanthurinae
Max. size:  45 cm SL (male/unsexed); max. reported age: 35 years
Environment:  reef-associated; marine; depth range 2 - 15 m
Distribution:  Indo-Pacific: East Africa, including the Mascarene Islands (Ref. 37792) to the Hawaiian and Society islands, north to Ryukyu Islands, south to Lord Howe Island.
Diagnosis:  Dorsal spines (total): 9-9; Dorsal soft rays (total): 25-27; Anal spines: 3-3; Anal soft rays: 24-25. Color in life bluish grey with numerous yellowish brown spots which tend to form irregular longitudinal lines; head with narrow irregular stripes; behind eye a yellow spot; brown pectoral fins; base of caudal fin with white bar. Caudal spine large, 3 - 4.4 in head. Stomach gizzard-like. Differs from A. dussumieri by having vertical stripes instead of spots on the blue central area of the caudal fin, from A. mata by having a lunate caudal fin, and from A. xanthopterus by having plain brown to blue-grey pectoral fins (Ref. 1602). The white ring around the base of the tail varies in intensity and may occasionally be absent (Ref. 1602).
Biology:  Adults occur in outer lagoon and seaward reefs, usually seen in small groups and school in some oceanic locations (Ref. 48637). Benthopelagic (Ref. 58302). They feed primarily on the algal film covering compacted sand, ingesting the usual component of sand which probably aids in the trituration of the algal food in the thick-walled stomach, also feed on diatoms and detritus (Ref. 3921).
IUCN Red List Status: Least Concern (LC); Date assessed: 03 May 2010 Ref. (130435)
Threat to humans:  harmless

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