Did You Know Piranhas Bark? Here's Your Chance to Hear It

Piranhas are like the rotweilers of the sea -- they bark and they bite. Scientists recently recorded piranhas barking and conclude these sounds mean back off -- now.

The fact that piranhas bark isn't new news to the scientific world but you usually have to pick them up to hear it -- and who's going to do that? Scientists at University of Liège, Belgium, were interested in recording why piranhas bark without outside stimuli. What they found is that it's a communication tool with each other, mostly meaning go away.

According to the release, scientists suspended a hydrophone and video camera into the piranhas' tank. They then compared the soundtrack with the movie they filmed finding that the fish were generally silent -- except in the face of confrontation.

Watch and hear piranhas bark in a tank:

"At first we thought there was only one sound," Parmentier said in the release, but then it became apparent that the piranhas produce two more: 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.

National Geographic reports more on deciphering piranha barks:

Parmentier and study co-author Sandie Millot of the University of Algarve in Portugal, though, used their tech-heavy technique to link three distinct sounds to three aggressive piranha behaviors.

A repetitive grunt was tied to a visual face-off, as if to say, "get away from me."

A second call resembling a low thud was associated with circling and fighting with other fish. Both of these calls, the researchers discovered, were made using a fast-twitching muscle that runs along a piranhas' swim bladder—an air-filled organ that helps fish maintain their buoyancy.

If fellow piranhas didn't heed these warning calls, the aggressor would begin chasing the neighboring fish and making a third type of sound by faintly gnashing teeth.

Interested in how these creatures make sound underwater? Scientists had previously known that the bark was associated with muscles attached to the fish's swim bladder. What they found was that it wasn't acoustic properties of the swim bladder resonating sound though, but the frequency with which the muscles attached to it vibrated.

It may be important to note, just for piranha's reputation, that only two or three of the 25 piranha species that exist in the wild pose a threat to humans, according to Parmentier.