The piranha warns before attacking

The second part of the study consisted of studying in what environmental conditions the piranha emits sounds. The equipment required for such a demonstration? A few piranhas (they can be obtained on the market), an aquarium, a hydrophone (in other words a waterproof microphone) and lots of...patience! The aim here was to link types of fish behaviour to characteristic sounds. After having studied at length the sounds and the images recorded, the Liège researchers identified three sounds manifestly linked to aggressive manoeuvres. The first of these manoeuvres is termed ‘frontal display.’ When two piranhas face up to each other they emit a kind of bark of intimidation. If that is not sufficient, the piranha begins to circle around its adversary and it produces a noise which can be likened to the beating of a drum. The final stage of the aggressive display consists of snapping its jaws. Contrary to the first two sounds, this one does not come from the swimbladder but from the mouth. And if all of these warning shots are not enough, then we have a real battle on our hands!

A new study under way at the Functional and Evolutive Morphology laboratory aims at studying the production of sounds according to the size of the piranhas. It was during one of these fish handling sessions that Sandie Millot had her finger gashed. ‘We also want to study the ultrastructure of the sonic muscles,’ explains Eric Parmentier.