Microphones lowered into a tank of aggressive red-bellied piranha revealed that the meat-eating fish bark at each other as an intimidation tactic before any fights broke out. They make drumbeat noises when they chase one another and more gentle croaking sounds when biting another piranha. 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 changing the frequency at which the muscles contract.
Previous research had found that piranhas produce noises using muscles attached to their swim bladders, but scientists weren’t sure how the swim bladder was involved in sound production. To find out, study researcher Eric Parmentier and his team stimulated the red-bellied piranhas’ swim-bladder muscles to contract.
Results showed that the swim bladder stopped vibrating as soon as the muscles finished contracting. This meant that the muscles were directly driving the swim bladder’s vibrations, the researchers said. The frequency, or pitch, of the bark and drum sounds was determined by the muscles’ contraction, not by any resonant properties of the swim bladder itself.
While the well-fed piranhas were generally peaceful, they occasionally attacked each other and even nipped at the researchers’ fingers.
Picture Credit : Google