Whitetail Surgeonfish

The Whitetail Surgeonfish, also called Thompson's Surgeonfish or the Night Surgeonfish, is a slender, dark-bodied tang in the family Acanthuridae. It is widely distributed across the Indo-Pacific, from East Africa to Hawaii and the Pitcairn Islands, typically found along outer reef slopes and drop-offs. Unlike most surgeonfishes, which graze algae from reef substrate, this species feeds primarily on zooplankton drifting above the reef, often forming large aggregations in open water near steep walls. Its uniform dark body paired with a contrasting pale tail makes it one of the more distinctive tangs to spot underwater. It is common throughout its range and is not considered threatened.

Field marks for the Whitetail Surgeonfish include:

• Slender, oval-bodied form in uniform dark brown to grey
• Sharply forked tail that is bright white to pale, strongly contrasting with the dark body
• Small, pointed snout
• Low, evenly rounded dorsal and anal fins
• Thin caudal spine typical of the genus

Adults reach roughly 22-26 cm. The stark two-tone pattern, dark body with a pale tail, readily separates it from other Acanthurus species, most of which show more complex banding or spotting. It is most often seen hovering in groups over reef drop-offs rather than close to the substrate.

This species favors outer reef slopes, drop-offs, and channels exposed to open water, typically at depths of about 10-40 m, where currents deliver zooplankton. Its range spans the tropical Indo-Pacific from East Africa and the Red Sea to Hawaii and French Polynesia, and from southern Japan south to the Great Barrier Reef and New Caledonia. Unlike shallow reef-crest specialists, it tends to occupy deeper, current-swept sites and is frequently seen well off the bottom in loose to large feeding aggregations. This open-water association distinguishes its habitat preference from more substrate-bound, algae-grazing surgeonfish relatives.

Whitetail Surgeonfish commonly form large feeding aggregations that hover in the water column just off reef drop-offs, picking zooplankton as it drifts past on currents, a strategy shared with only a handful of other tangs. Activity typically peaks around dawn and dusk, when plankton density near reefs increases. Outside of feeding periods, individuals retreat toward reef structure for shelter. As with other Acanthuridae, the caudal spine provides defense against predators when threatened. Spawning follows a broadcast pattern, with adults releasing eggs and sperm into open water, and larvae developing pelagically before settling onto reef habitat as juveniles.