Triggerfishes (Balistidae) are so called because of the triggerlike mechanism controlling the large first dorsalfin spine on the top of their head. Once this spine is locked in an erect position, which the fish does in order to wedge itself into crevices in the coral where it cannot be dislodged by a predator, the spine cannot be pushed down until the short “trigger” spine behind it is depressed. The family name Balistidae is derived from the Latin ballista, another name for the Roman catapult, in allusion to the trigger mechanism of the dorsal-fin spines.
Triggerfish are mostly found on coral reefs, and when under threat they dart into a hole or crevice on the reef, lock their dorsal spine erect and wedge themselves into the reef. They also possess extremely tough skin consisting of hard, platelike scales. Most are solitary and feed on coral or hard-shelled invertebrates which are crushed with their strong teeth. Although they have relatively small mouths, they have strong, sharp teeth, and can deliver a painful bite. The diet consists a variety of benthic invertebrates, including crustaceans, molluscs, brittlestars, tunicates, sponges, hydrozoans, tips of branching coral, and small fishes. Sea urchins are a favourite food, and even the long spines of sea urchins pose no problem for a hungry triggerfish. The fish just picks the sea urchin off the bottom, flips it over in midwater and then feeds on the unprotected underside of the urchin. A few species, including the black triggerfish, feed primarily in the water above the reef on large zooplankton or drifting algae that has been detached from the reef.
The ocean triggerfish, (Canthidermis sufflamen) can be found at depths ranging from near the surface to 60m. It is brownish grey, a large dark brown spot at the base of the pectoral fins, and grows to 65cm. This species is another large zooplankton feeder.
There are over 40 species of triggerfish, but only a few species will be found in these waters, and these are listed below, along with their maximum adult length:
- Black Triggerfish Melichthys niger 50cm
- Blackbar Triggerfish Rhinecanthus aculeatus 30cm
- Bluespotted Triggerfish Balistes punctatus 60cm
- Grey Triggerfish Balistes capriscus 60cm
- Ocean Triggerfish Canthidermis sufflamen 65cm
- Queen Triggerfish Balistes vetula 60cm
- Spotted Oceanic Triggerfish Canthidermis maculata 50cm