Ringtail Surgeonfish

The Ringtail Surgeonfish, also called the Bloch's surgeonfish, is a mid-sized member of the family Acanthuridae found across the tropical Indo-Pacific. It ranges from the coast of East Africa eastward to Hawaii and the Pitcairn Islands, and from southern Japan south to Lord Howe Island. First described in 1835, the species is named for the pale ring encircling the narrow base of its tail, a feature that distinguishes it from closely related surgeonfishes. It is a common, non-threatened reef species frequently encountered by divers on shallow to moderately deep coral and rocky reefs, where it grazes algae alongside other herbivorous fishes in mixed feeding groups.

Look for these traits to identify the Ringtail Surgeonfish:

• Deep, oval body in dusky blue-grey to purplish-brown
• Faint pale vertical bars sometimes visible on the flanks
• A conspicuous narrow white ring at the base of the tail, just ahead of the fin
• Lunate, yellow-orange tail fin
• Single sharp spine that folds into a groove near the tail

Adults grow to about 45 cm. The white caudal ring is the most reliable field mark, separating it from similarly colored Acanthurus species such as the Yellowfin Surgeonfish, which lacks this pale band and instead shows a yellow pectoral patch.

Ringtail Surgeonfish occupy coral and rocky reefs, reef flats, and lagoons throughout the Indo-Pacific, typically at depths from about 2 to 15 m. Their range spans from East Africa and the Red Sea east to Hawaii and French Polynesia, and north to the Ryukyu Islands of Japan. They favor areas with a mix of live coral, rubble, and algal turf, often patrolling reef edges exposed to moderate wave action. Juveniles tend to settle in shallower, more sheltered nearshore habitats before moving to deeper reef zones as they mature. The species tolerates a range of reef conditions, contributing to its wide and stable geographic distribution.

This surgeonfish is often observed feeding in loose to large mixed-species schools alongside other herbivorous tangs, a strategy that helps overwhelm the territorial defenses of damselfish guarding algal turf patches. It grazes primarily during daylight hours, using its small mouth to scrape filamentous algae from reef substrate. Outside of feeding schools, individuals may hold loose territories on the reef. Like other Acanthuridae, it defends itself by slashing with the sharp caudal spine when cornered. Reproduction follows a broadcast-spawning pattern, with adults gathering at reef edges around dusk to release eggs and sperm into the water column, where fertilized eggs drift as plankton before larvae settle onto reef habitat.