Triggerfish - Anatomy and Appearance

Anatomy and Appearance

The largest member of the family, the stone triggerfish (Pseudobalistes naufragium) reaches 1 metre (3.3 ft), but most species have a maximum length between 20 and 50 centimetres (7.9 and 20 in).

Triggerfish have an oval shaped, highly compressed body. The head is large, terminating in a small but strong- jawed mouth with teeth adapted for crushing shells. The eyes are small, set far back from the mouth, at the top of the head. The anterior dorsal fin is reduced to a set of three spines. The first spine is stout and by far the longest. All three are normally retracted into a groove. The ventral and the posterior dorsal fins are capable of undulating from side to side to provide slow speed movement. The sickle shaped caudal fin is used only to escape predators.

The two pelvic fins are overlaid by skin for most of their length and fused to form a single spine, terminated by very short rays, their only external evidence. Gill plates operculum too, although present are not visible, overlaid by the tough skin, covered with rough, rhomboid scales, that forms a stout armor on their body. The only gill opening is a vertical slit, directly above the pectoral fins. This peculiar covering of the gill plates is shared with other members of the Tetradontae order. Each jaw contains a row of four teeth on either side, while the upper jaw contains an additional set of six plate-like pharingeal teeth.

As a protection against predators, triggerfish can erect the first two dorsal spines: The first, (anterior) spine is locked in place by erection of the short second spine, and can be unlocked only by depressing the second, “trigger” spine, hence the family name “triggerfish”.

With the exception of a few species from the genus Xanthichthys, the sexes of all species in this family are similar in appearance.