One of the prettiest and, in some places, most conspicuous fish to be observed swimming around the edges of a reef is the bright-blue red-toothed triggerfish Odonus niger. Fanning undulating dorsal and anal fins, and trailing a gorgeous lyre-shaped tail, this beautiful triggerfish belongs to the family Balistidae, of which there are roughly 40 species.
Arguably, the species’ most unique feature, provided you can get a close enough look, are the sharp, protruding red teeth that develop their colour as the individual matures. Growing to a healthy size of 50cm, these characterful creatures are common residents of sloping, current-swept reefs throughout the Indo-Pacific. In some cases, they can darken the water column as thousands of individuals gather to feed on morsels of passing zooplankton.
Another characteristic feature of triggerfish is their response to danger. When threatened, their immediate reaction is to move toward a sheltering crevice in the reef wall. Swimming head-first into their hole, they engage their 007 dorsal-spine-gadget! The long and sturdy first dorsal spine is erected and locked into place by a shorter, second spine, the base of which slots into a groove in the first spine. Having these rigid, interlocking spines firmly fixed in this position prevents any pesky predator from pulling them out of their holes. Divers unfamiliar with this defensive tactic are often perplexed when they find strange blue tails protruding from the reef. Only once the triggerfish feels confident that the coast is clear will it depress the second dorsal spine – the ‘trigger’ – allowing the first spine to fold down so that it can wiggle out backwards.
Some scuba divers associate triggerfish with the more aggressive habits of some of the sub-species, which are known for being especially fierce, particularly when guarding their nests on the seafloor.
The titan triggerfish Balistoides viridescens attains sizeable lengths of up to 75cm and sports large canine teeth for ripping into reefs to uncover cowering sea urchins and brittle stars. The eggs are laid within a depression blown into the sand and any approaching intruder must beware of the explosive reactions of the guardian parent. As the territory is cone-shaped, expanding upwards from the nest, the best tactic to avoid serious bites to the fins or body is to swim away in a horizontal direction.
Fortunately, most of the smaller species do not demonstrate such aggressive behaviour. In fact, Hawaii has chosen a glamorous triggerfish as its state fish: the wedge-tail triggerfish. For those into party games, you might invite your guests to try pronouncing its Hawaiian name – humuhumunukunukuapua`a! There are likely to be a few tongues needing untying after that …
Whatever their names, it is clear that the triggers are stand-out members of reef society.