Tenacious Triggerfish: The Territorial Reef Residents

Triggerfish are one of the few groups of fish with a reputation for being temperamental and aggressive but are also known for their tenacity and their important role in the marine ecosystem. They are brightly coloured, oval-shaped, and marked by conspicuous lines, bands, and dots. Sporting shades of blue, green, yellow, and red, their complex palette helps them recognise, communicate with, and signal each other, while setting them apart as a different group.

Triggerfish are found in warm seas across the world and thrive in habitats with a variety of substrates, including coral, seagrass, sand, rock, and algae. Though mostly found in shallow coastal waters, a few species are entirely pelagic (live in open seas). Most of the 40 triggerfish species recorded worldwide are found in the Indo-Pacific region, which hosts more than 70 per cent of the world’s marine biodiversity.

The “trigger”

Triggerfish belong to the order Tetraodontiformes, which is characterised by the presence of four plate-like teeth (tetra = four; odontus = teeth). The triggerfish family Balistidae takes its name from the Latin word “balista” which roughly translates to “crossbow” — a reference to the dorsal spines on top that lock into place (in response to threats) or lie flat in a groove. These spines, with their locking and unlocking motion, like a trigger, give triggerfish their common name.

In response to threats, triggerfish erect their spines to intimidate predators and firmly anchor themselves under rocks or in crevices. They can be extremely aggressive, especially around nests or territories, often chasing away or charging at divers and other intruders, and delivering a painful bite in extreme cases. While most triggerfish species are too small to cause real damage, large ones like the titan triggerfish (Balistoides viridiscens) are best avoided.

Prey and predation

Triggerfish mainly feed on benthic (sea floor) invertebrates, including molluscs, sea urchins, polychaete worms, crustaceans, and sometimes on algae. They have a large head that tapers into a small mouth with strong jaws. The teeth are large and typically plate-like, and each jaw has two rows or plates of four teeth each — making up eight outer teeth in each jaw. As with all fish that feed on hard, calcareous substances like corals and shells, triggerfish have a set of strong pharyngeal (in the throat) teeth that break down hard mollusc shells.

Using their fins, they fan away the sand to expose prey, picking them out using their small but strong jaws that can crack most hard shells. They flip over sea urchins, attacking and smashing the exposed underside where there are fewer spines. Triggerfish usually leave debris in the wake of their feeding frenzy, attracting many smaller fish to hang around to scavenge on the titbits strewn around.

The size of a triggerfish varies by species, with most individuals averaging between 15-25 cm. The Picasso triggerfish (Rhinecanthus aculeatus) is one of the smallest triggerfish species. The largest triggerfish in the world is the stone triggerfish (Pseudobalistes naufragium) growing up to 100 cm, followed by the titan triggerfish (Balistoides viridescence) with a maximum recorded size of 75 cm (and considered the largest in the Indo-Pacific region).

Triggerfish are preyed upon by large groupers, jacks, tunas, and sharks. The larger, more aggressive triggerfish may use their size to their advantage and take on large groupers to defend themselves.

Reproduction and territoriality

Triggerfish are mostly solitary and will aggressively defend their territories, though they may appear to swim as a group because of their common feeding grounds. Some triggerfish species organise into a harem socially, with one male defending several females in his territory. As with other marine species, triggerfish spawn according to a lunar and tidal timetable.

Males typically travel to traditional spawning grounds, maintain territories there, and build hollow nests in the ground. They defend their territories, and the females collectively care for a shared nest of eggs until they hatch. Females “tend” to the eggs, fanning and blowing water on the eggs to oxygenate them. Once they hatch, the females usually leave the nest territory.

Triggerfish live up to 8-13 years on average, but this can go to 20 years in captivity. They typically attain sexual maturity at around 2 years.

Surviving change

Like all other marine animals, triggerfish too, have a role to play in the marine ecosystem. Some species, like the orange-lined triggerfish (Balistapus undulatus), help keep populations of reef-eroding sea urchins in check, helping coral health. Species that feed on algae prevent the algae from growing over coral. Triggerfish take on the role of keystone species in some sub-tidal algal food webs. A keystone species usually plays a critical role in holding the ecosystem in balance.

Loss and destruction of their habitats, the aquarium trade, poorly regulated game fishing, and destructive fishing practices are some of the key threats triggerfish face. Vibrantly colourful species like the clown triggerfish (Balistoides conspicillum) and queen triggerfish (Balistes vetula) are often fished to be sold at lucrative prices in the aquarium trade.

While not considered commercial fish, in certain parts of the world, some triggerfish are sought for their light, white meat. Species like the red-toothed triggerfish (Odonus niger) are fished for their protein content and used to manufacture fish protein powder (FPP). Small juveniles are sometimes used as bait by artisanal fishers. 

Adaptable enough?

Triggerfish are incredibly adaptable. Their hardiness, coupled with a broad, variable diet and affinity for a range of habitats, ensures their survival in oceans affected by climate change. However, even the superpower of adaptability is not enough to save these unique fish from sustained and rapidly increasing threats. While most of the species are not significantly threatened, populations of several species from the Balistes genus are declining globally.

Triggerfish are curious and bold; they will inspect and likely attack anything that snags their attention. Despite their infamous reputation for being grumpy, their tenacity and temperament, while of concern to unsuspecting divers, contribute towards their resilience. Observing their peculiar foraging behaviour without encroaching on their space is as rewarding as observing any other charismatic marine species. The reefs would be a quieter, emptier space without triggerfish; they are an important part of the puzzle that is the complex marine food web.