SurgeonfishesAcanthuridae

Surgeonfishes are oval, laterally compressed reef fishes, named for the sharp, retractable, scalpel-like spine on each side of their caudal peduncle. These fishes typically measure between 15 and 38 cm (6-15 inches), though some species grow larger. They possess a continuous dorsal fin and a small mouth. Body coloration varies widely among species, often featuring shades of blue, yellow, orange, or brown, with many displaying intricate patterns or vertical stripes.

These diurnal fishes are commonly encountered on shallow reef flats, slopes, and drop-offs, found down to at least 40 m (130 ft). Primarily herbivorous, they graze on benthic algae using their specialised teeth and small mouths, the shape of which varies across species, adapted for different algal types. Many species form large, often transient, schools that roam across the reef, while others are solitary or live in small groups, defending feeding territories. The caudal spine can be quickly extended for defence against predators or rivals.