Researchers eavesdrop on piranhas as they squabble over food, square up for a fight and bite each other

Recordings of piranha fish squabbling over morsels of food reveal that there is much more to the meat-eaters than their famous bite.

Microphones lowered into a tank of aggressive red-bellied piranha picked up an impressive repertoire of barks, croaks and drumbeat sounds, each of which is thought to convey a different message.

Though silent most of the time, the fish broke into aquatic barks at the first sign of trouble, such as when they confronted other fish over lunch, or were – cautiously – handled by researchers.

Fish are known to use sounds to communicate, and especially to attract a mate, but the variety of noises and their meanings is poorly understood.

Eric Parmentier, at the University of Liège, in Belgium, used hydrophones and a video camera to record the piranha as they cruised around their tank and occasionally competed for food.

The footage revealed that the piranha barked at each other as an intimidation tactic before any fights broke out. They made drumbeat noises when they chased one another and more gentle croaking sounds when biting another piranha.

The study was not without its hazards for Parmentier and his colleague, Sandie Millot. "We both visited the hospital because we were bitten and Sandie's finger was nearly cut in half," Parmentier said.

Like other vocal fish, piranha produce sounds by rapidly tensing muscles connected to their swim bladders, the organ used to control buoyancy. The fish alter the pitch of their croaks and barks by the changing the frequency at which the muscles contract.

Parmentier and his colleagues describe the study in the latest issue of the Journal of Experimental Biology. The piranha were kept in small groups in a tank in the researchers' laboratory.

Adult red-bellied piranha grow up to 30cm (1ft) long and have a single row of teeth on their upper and lower jaws. Their bite is effective at puncturing and tearing flesh because their teeth are shaped like sharp blades and they interlock when the jaws close.

The fish pick up sounds as they travel through the water using the lateral line. This sensory organ picks up changes in water pressure, currents and the movements of other animals in the water.

While piranha live in shoals, they do not hunt in an organised manner. The feeding frenzies they are associated with occur only when starved shoals encounter a rare feast in the form of a stricken animal in the water.

Other fish produce sounds to lure mates into nests and defend their territories. In 2008, Andrew Bass, at Cornell University, in New York, recorded nocturnal toadfish and closely-related midshipman fish, and found that the males made a deep humming sound to attract females into their lairs, but saw off intruders with short, sharp, grunts.

Examinations of the parts of the fish brain controlling the pitch and duration of their calls have led scientists to track the origins of vocal communication back in time along the evolutionary tree.

Having eavesdropped on hours of aggressive piranha chatter, Parmentier's team now hopes to record more amorous piranha in Brazil. "It is difficult for the fish to reproduce in the tank, so I am sure we have to deploy hydrophones in the field to [get] the sounds produced during mating," Parmentier said.