Yellowfin Surgeonfish

The Yellowfin Surgeonfish, sometimes called the Yellowmask or Cuvier's Surgeonfish, is one of the largest members of the family Acanthuridae, reaching up to 70 cm in length. It occurs throughout the Indo-Pacific, from East Africa to Hawaii and the eastern Pacific coast of the Americas, and has even been recorded from the Mediterranean via the Suez Canal. First described in 1835, this species undergoes a notable color change with age, with juveniles and adults differing enough in appearance that they were once classified as separate species. It typically inhabits lagoons, bays, and reef edges rather than exposed outer reef walls, and is a common, non-threatened species across its wide range.

Key identification points for the Yellowfin Surgeonfish:

• Large, deep, oval body in grey-brown to purplish tones
• Faint pale vertical bars sometimes visible on the flanks
• Bright yellow patch spanning the base of the pectoral fins
• Blue ring around each eye
• Lunate tail and a prominent caudal spine set within a pale oval patch

Adults commonly reach 50-70 cm, notably larger than most reef-associated tangs. The yellow pectoral-fin patch is the clearest field mark separating it from the similarly colored Ringtail Surgeonfish, which instead shows a white ring at the tail base.

Yellowfin Surgeonfish inhabit lagoons, sandy-bottomed bays, seagrass edges, and reef flats across the tropical and subtropical Indo-Pacific, from East Africa and the Red Sea to Hawaii, and into the eastern Pacific off Mexico and Central America. They are typically found at depths from the shallows down to about 90 m, often over open sand or rubble adjacent to reef structure rather than dense coral. This species tolerates a broader range of substrate types than many surgeonfishes, including turbid coastal waters, contributing to its unusually wide geographic distribution across two ocean basins.

This large surgeonfish feeds on a mixed diet of filamentous algae, detritus, diatoms, and occasionally small invertebrates, often foraging over open sand and rubble rather than dense coral. It may be seen solitarily, in pairs, or in loose schools, particularly over feeding grounds in lagoons and bays. Juveniles and adults display markedly different coloration, a pattern of ontogenetic color change seen in several surgeonfish species. Like other Acanthuridae, it uses a sharp caudal spine for defense. Spawning occurs via broadcast release of eggs and sperm into open water, typically timed around dusk, with pelagic larvae dispersing before settling onto suitable habitat.