Brown Surgeonfish

The Brown Surgeonfish is a small, abundant member of the family Acanthuridae found across the Indo-Pacific and Red Sea. Despite its plain coloration, it is ecologically important as one of the most common algae-grazing fish on many Indo-Pacific reefs, playing a significant role in controlling algal growth on reef substrate. First described in 1775, it ranges from the Red Sea and East Africa to Hawaii and French Polynesia. Its unremarkable brown appearance sets it apart from many showier reef tangs, but its sheer abundance and grazing activity make it a key contributor to reef ecosystem function. It is common and not considered threatened.

Identify the Brown Surgeonfish by these traits:

• Small, oval body in uniform dusky to grey-brown
• Faint wavy blue-grey lines across the head
• A small orange spot near the spine base on the caudal peduncle
• Low, continuous dorsal fin running the length of the back
• Dark, lunate tail fin

Adults reach only about 18-21 cm, notably smaller than most other Acanthurus species. Its plain brown body with subtle head markings and small orange peduncle spot distinguishes it from more boldly patterned relatives such as the Lined or Eyestripe Surgeonfish.

Brown Surgeonfish occupy shallow reef flats, lagoons, and rocky reef edges throughout the Indo-Pacific and Red Sea, generally in less than 15 m of water. Their range spans from the Red Sea and East Africa eastward to Hawaii and the Pitcairn Islands, and from southern Japan south to the Great Barrier Reef. They favor areas with dense algal turf growth on hard substrate, including reef flats subject to moderate wave exposure. Because of their tolerance for a wide range of shallow reef conditions, they are frequently among the most numerically dominant herbivorous fish observed on Indo-Pacific reef surveys.

This species is a highly active diurnal grazer, often observed in large, loosely coordinated feeding schools that move across reef flats cropping algal turf. Schooling in numbers is thought to help individuals overcome the territorial defenses of damselfish guarding algae patches. Outside of active feeding bouts, individuals may disperse and hold loose space on the reef. As with other Acanthuridae, the caudal spine is used defensively when an individual is threatened or handled. Reproduction follows a broadcast-spawning strategy, with large numbers of adults sometimes gathering at reef edges around dusk to release eggs and sperm synchronously into the water column.