Scientists have recently discovered that the widely feared piranha, use sounds to communicate with one another in an attempt to intimidate rivals, instead of attacking them.

Dr Eric Parmentier, from the University of Liege, Belgium, previously studied sound production and communication in a variety of fish species including piranhas. This research discovered that piranhas made sounds, however was inconclusive as to why. Studies in this area suggest that a wide variety of fish use noises to attract potential mates, therefore the sounds made by piranhas could possibly indicate a reproduction process.

Through the use of hydrophones (underwater microphones), Dr Parmentier and his colleagues undertook a laboratory experiment that recorded the sounds piranhas made when they confronted each other, while also filming their interactions.

The recordings picked up three distinct sounds from the piranhas. The first was a bark that the fish produced when they “displayed” or confronted one another without engaging in fighting behaviour. The other two were a drum – like beat which they used when chasing one another and a softer croak made when biting other individuals. These physical confrontations tended to be made over food.

For much of the study the fish made no noise and did not engage in any passive or physical confrontations. It was only after hours of observations that researchers managed to capture this illusive behaviour.    

The production of sound in piranhas is made by vibrating their swim bladders, a gas filled chamber that helps regulate their buoyancy. The vibration of the swim bladder is driven by high speed muscles that contract and relax 150 times every second.

Dr Parmentier suggests piranhas use noises to communicate as it uses less energy than physical conflicts. As a result, energy expenditure can be directed into other important biological activities such as reproduction and feeding.

Dr Parmentier and his team are aiming to conduct further studies on piranhas in the Amazon to find out more about the acoustic repertoire of this fascinating creature.