Triggerfish include about 40 different species of brightly colored fish from the family, Balistidae, which inhabit tropical and subtropical oceans throughout the world. The greatest number inhabiting the Indo-Pacific.
Most triggerfish are found in relatively shallow waters, especially on coral reefs, but some, such as the oceanic triggerfish (Canthidermis maculata), are pelagic fish. Triggerfish have a very distinctive shape and have an oval highly compressed body with a large head terminating in a small but strong jawed mouth used mainly for crushing hard shelled invertebrates. The eyes are set quite far back from the mouth and operate independently of one another. The anal and posterior fins are mainly used for locomotion, undulating to provide movement. Only when stressed or wishing to escape from a predator will the caudal fin be used for locomotion.
The anterior dorsal fin is reduced to three spines with the first spine being the largest. All three spines are normally retracted into a groove. For protection against predators they can erect the first two dorsal spines; the first (the anterior) spine is locked in place by erection of the shorter second spine, and can be unlocked from its vertical position only by lowering the second, “trigger” spine, hence the name “triggerfish”.
The triggerfish’s skin is thick and tough, providing protection against predators and parasites alike.
Some species can be very aggressive towards divers when nesting. The males guard the area around their eggs, an area that extends both upward and horizontally in a dome shape. The area may contain nest eggs with more than one female, making the guarded area quite large. The worst culprits are the titan triggerfish (Balistoides viridescens), which, because of their size, can deliver a very painful bite and even take chunks out of a divers fins. The smaller picasso trigger fish is also quite aggressive when nesting but, due to its smaller size, is not as capable of doing the damage its larger cousin can.
When confronted with a defensive triggerfish it’s best to swim away from it horizontally in the opposite direction from that in which it is coming. A particularly aggressive triggerfish may follow a diver for some distance anyway, attempting to nip the diver on his extremities, however, this is not very common. Perhaps the best tactic is to swim backwards away from the fish presenting ones fins for biting rather than any body part. Some divers have resorted to taking off a fin and waving it at the fish to chase it away when they persist after one has left the immediate area.
Only the smaller species are generally kept in home aquariums and care has to be taken when choosing them and their tank mates.