Triggerfishes are members of the family Balistidae of the order Tetradontiformes. They derive their name from a unique feature of their dorsal fin. The triggerfish can lock the large dorsal spine in an upright position by supporting it with its smaller secondary spine. This protects the fish from predation by larger fish because the erect spine makes the fish hard to swallow or extract from small crevices. The locked dorsal spine can be "un locked" by depressing the third spine or "trigger" which is connected to the second spine.
A distinctive characteristic of triggerfish is similarity in size and shape of the second dorsal (back) and anal fins. The belly in front of the anal fin is the widest circumference of the fish. The body of the triggerfish is protected by bony plates.
Triggerfishes are moderately large fish generally found on coral reefs widely distributed throughout the world, in all about 36 species. The gray triggerfish, Balistes capriscus, averages under 1 ft (0.3 m) in length but may grow to 2 ft (0.6 m) with a weight of 3 lb (1.4 kg). It is found in the warm waters of the Gulf of Mexico and the Mediterranean. These grayish fish often appear spotted or splotchy when swimming in among seaweeds.
Among the largest in the family is the ocean trigger-fish, Canthidermis sufflamen, which grows to 2 ft (0.6 m) and weighs about 10 lb (4.5 kg). It ranges in distribution from the coast of Florida to the Caribbean. The ocean triggerfish is capable of making sounds like some of its relatives. One of the ways it makes sound is by vibrating some muscles that are attached to its swim bladder.
Several species, such as the redtail triggerfish, are found in the western Pacific. The redtail Xanthichthys mento is a 10 in (25 cm) fish with a purplish blue color and a red tail. In contrast to the redtail triggerfish, the Abalistes stellaris may grow to 24 in (60 cm) in length.