London: Aggressive piranhas also resort to `barking` to keep intruders at bay, besides administering vicious bites.
But that didn`t deter Sandie Millot, Pierre Vandewalle and Eric Parmentier, researchers from the University of Liege, Belgium.
"You just have to pick them up and they make sounds," says Parmentier. However, it wasn`t clear when and why piranhas produce sounds naturally.
Intrigued by the mechanisms they use to generate sound, the team monitored the behaviour of small groups of captive red-bellied piranhas to discover that they have a repertoire of three combative sounds, The Journal of Experimental Biology reports.
Suspending a hydrophone in the piranhas` tank, Millot and Parmentier recorded the fish`s sounds and filmed them as they cruised around and competed for food, according to a Liege statement.
According to Parmentier, the well-fed fish were relatively peaceful -- attacking each other occasionally -- although they were not averse to nipping at near-by fingers.
"We both visited the hospital because we were bitten and Sandie`s finger was nearly cut in half,` recalls Parmentier.
The team found that the fish were generally silent, but they vocalised as soon as they entered into a confrontation -- producing the same barking sound that they did when held in the scientists` hands.
"At first we thought there was only one sound," admits Parmentier, but then it became apparent that the piranhas produce two more.
They are "a short percussive drum-like sound when fighting for food and circling an opponent; and a softer `croaking` sound produced by their jaws when they snap at each other".