Triggerfish swim to their own beat

Triggerfish use their fins, scales and swim bladder to make their own percussion, scientists at the University of Liège in Belgium say. The noise they make can be best likened to a relatively loud drum roll. At three centimetres away, this sound comes in at a 136 decibels under water.

The fish make this noise by swishing their fins and forcing scutes – similar to scales – against their swim bladder, which is a pocket of air to help the fish float through water, the researchers say in the study published in The Journal of Experimental Biology.

As juvenile fish grow older the dominant frequency of the drum roll decreases as their bodies get bigger, the researchers say. Once they reach adulthood their drum roll stays at roughly the same pitch even if the fish grow very large.

Exactly why triggerfish make drum roll sounds is not yet clear, study co-author Loïc Kéver, an evolutionary biologist at the University of Liège, told IBTimes UK. "It's not a complete mystery but it's not completely answered. We think it's a distress call. It's maybe to scare a predator. It's generally produced when the fish is stressed, for example, when we hold the fish in our hands."

All kinds of triggerfish make drum roll sounds, Kéver says, old and young, male and female. But there may be subtleties in the kinds of noises that different species and types of fish that the researchers hope to tease out in further research.

This peculiar fish – which has many nicknames, including the Picasso fish due to its bold colouring – can grow up to about 30 centimetres long and lives in the Indian Ocean and the Pacific Ocean. The triggerfish belongs to the Balistidae family of fish, which is known for its strange noises. It's thought that some Balistidae species make a characteristic noise by grinding or bashing their teeth.