Doubletooth Surgeonfish

The Doubletooth Surgeonfish is a common name applied to members of the genus Prionurus, sometimes called sawtail surgeonfishes, within the family Acanthuridae. The representative species, Prionurus biafraensis, is restricted to rocky and coral reefs of the eastern tropical Atlantic, from the Gulf of Guinea to Sao Tome. Like other tangs, it is a deep-bodied, laterally compressed reef fish related to the more familiar Indo-Pacific surgeonfishes and unicornfishes. The genus name references the row of forward-angled, tooth-like bony keels running along the caudal peduncle, distinct from the single retractable spine found in most Acanthurus species. It is not currently considered threatened, though its range is limited and localized compared to its wide-ranging Indo-Pacific relatives, making regional population data comparatively scarce.

Key features for recognizing this sawtail surgeonfish:

• Oval, laterally compressed body in olive-grey to dusky brown, paler below
• Small, comb-edged mouth adapted for grazing algae
• Several forward-curved bony ridges ('teeth') along the caudal peduncle instead of one blade-like spine
• Long, low dorsal and anal fins running most of the body length
• Forked, yellowish tail

It is best told apart from single-spined Acanthurus species by the multiple raised keels near the tail base, and from Naso unicornfishes by lacking a forehead horn or knife-like caudal spines. Body size stays modest, typically 30-50 cm, smaller than the largest Indo-Pacific tangs.

Doubletooth (sawtail) surgeonfishes occupy shallow rocky and coral reef habitats, generally from the surface down to about 20-30 m. The representative species is confined to the eastern tropical Atlantic, occurring along the Gulf of Guinea coast from Gabon to the Republic of Congo and around offshore islands such as Sao Tome. It favors clear, current-swept reef edges and rocky outcrops where algal turf is abundant, similar to the preferences of related sawtail species found off Australia, Japan, and the eastern Pacific. Water temperatures in its range stay warm year-round, and adults are usually seen close to structure rather than in open water.

Sawtail surgeonfishes are primarily diurnal grazers, using their comb-like teeth to rasp algal turf from rock and reef surfaces. Individuals may be solitary or form loose aggregations, and some related Prionurus species gather in large schools when feeding or spawning, a behavior thought to reduce risk from territorial damselfish defending algal patches. Like other Acanthuridae, they can flex the caudal peduncle sideways to slash rivals or predators with their bony keels when threatened. Spawning follows a broadcast pattern typical of the family, with pelagic eggs and larvae dispersing before settling onto reef habitat. As algae grazers, they help limit algal overgrowth on reef substrate, contributing to space for coral recruitment.