A plain brown grazer with orange freckles on the face; abundant and routinely passed over.
To about 21 cm, dull brown with a lavender or purplish cast, scattered small orange-red spots over the head and the front of the body, a black spot at the rear base of the dorsal fin and a matching one at the rear base of the anal fin, and a pale tail base. The common name applied to this fish in some sources is blue-lined surgeonfish, which properly belongs to Acanthurus nigroris, a different and much less frequently recorded species here; brown surgeonfish is the accepted name for A. nigrofuscus.
Two other plain brown fish share its ground. The striated surgeonfish Ctenochaetus striatus is finely lined horizontally, has no orange freckling and lacks the paired fin-base spots. The brown tang Zebrasoma scopas is a different shape altogether, with a high sail-like dorsal and anal fin and a patch of bristles on the tail base. Checking the head for orange spots separates A. nigrofuscus from both.
It grazes filamentous algae off rock, dead coral and rubble, often in loose aggregations of several dozen that move along the shallow reef together and occasionally swamp a damselfish’s territory in numbers to feed inside it. Because it needs only hard substrate and algal turf rather than living coral, it is one of the surgeonfishes that stays common right through the muck destinations. Recorded from about 1 to 30 m, mostly in the top 15.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.