Acanthuridae

Acanthuridae are a family of ray-finned fish which includes surgeonfishes, tangs, and unicornfishes. The family includes about 86 extant species of marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular in aquaria.

The family name comes from Ancient Greek ἄκανθα (ákantha), meaning "spine", and οὐρά (ourá), meaning "tail", a reference to the scalpel-like bony plates on the type species' caudal peduncle. In the early 1900s, the family was called Hepatidae.

Acanthuridae contains the following extant subfamilies and genera:

There are several extinct genera known from fossils dating from the Eocene to Miocene:

A particularly large diversity of fossil surgeonfish is known from the Monte Bolca lagerstatte of Italy. These represent some of the earliest representatives of the individual tribes within the Acanthuridae.

The distinctive characteristic of the family is that they have scalpel-like modified scales, one or more on either side of the peduncle of the tail. The spines are dangerously sharp and may seriously injure anyone who carelessly handles such a fish. The dorsal, anal, and caudal fins are large, extending for most of the length of the body. The mouths are small and have a single row of teeth adapted to grazing on algae.

Surgeonfishes sometimes feed as solitary individuals, but they often travel and feed in schools. Feeding in schools may be a mechanism for overwhelming the highly aggressive defense responses of small territorial damselfishes that vigorously guard small patches of algae on coral reefs. Most species are fairly small, with a maximum length of 15–40 cm (6–15.5 in), but some in the genus Acanthurus, some in the genus Prionurus, and most species in the genus Naso may grow larger; the whitemargin unicornfish (Naso annulatus) is the largest species in the family, reaching a length of up to 1 m (3 ft 3 in). These fishes may grow quickly in aquaria, so average growth size and suitability should be checked before adding them to any marine aquarium.

A larval acanthurid, known as an acronurus, looks strikingly different from the juvenile and adult forms of the same individual. It is mostly transparent and tends to have a pelagic lifestyle, living in open water for an extended period of time before settling on the ocean bottom near the shore, where it develops into the juvenile and ultimately the adult form.