Naso thynnoides (Cuvier, 1829)
Oneknife unicornfish
Naso thynnoides
photo by Greenfield, J.

Family:  Acanthuridae (Surgeonfishes, tangs, unicornfishes), subfamily: Nasinae
Max. size:  40 cm FL (male/unsexed)
Environment:  reef-associated; marine; depth range 2 - 40 m
Distribution:  Indo-Pacific: East Africa to Micronesia (excluding the Marshall Islands), north to the Ryukyu Islands, south to the Solomon Islands and the Great Barrier Reef. Range extending to Rangiroa Atoll, Tuamotu Archipelago.
Diagnosis:  Dorsal spines (total): 4-4; Dorsal soft rays (total): 28-30; Anal spines: 2-2; Anal soft rays: 27-29. Body elongate-ovate. Dorsal and anal profiles nearly even. Forehead without rostral prominence when in adults. Peduncular plate single, with a semicircular, retrorsely curved keel. Reaches 35 cm SL. Description: Characterized further by overall pale grey body color; side of body with broad yellowish zone and numerous thin bluish-grey bars; greatest depth of body 2.8-3.2 in SL (Ref. 90102).
Biology:  Generally uncommon species found in steep outer lagoon and seaward reef slopes (Ref. 9710, 48637). Maximum depth reported at 40m (Ref. 37792) Occurs singly or in large schools (Ref. 9710, 48637). Usually seen swimming steadily along upper edges of drop-offs in pursuit of plankton (Ref. 48637). A semi-pelagic fish that feeds on zooplankton, but remains over or near reefs. Also feeds on algae (Ref. 30573). It is cleaned by Labroides and sleeps on reefs at night, taking on a disruptive mottled pattern (Ref. 10671). Caught with nets (Ref. 30573).
IUCN Red List Status: Least Concern (LC); Date assessed: 06 May 2010 Ref. (130435)
Threat to humans:  harmless
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