Like a pit bull, piranhas will tear the flesh from your bones. Also like a pit bull, they bark. [piranha audio type 1] Kind of.

Scientists had known that piranha barked when you pick them up—carefully, of course. But they hadn’t known what these sounds were for. So researchers examined how the vocalizations might correspond with behavior.

They dropped a microphone into a piranha tank that, at different times, held three groups of 10 fish. They then placed a mussel in to see how the fish competed for food.

When the fish faced off, they produced that percussive bark. [piranha audio type 1]

When they circled one another, they made a softer thud sound. [piranha audio type 2]

A teeth-gnashing [piranha audio type 3] indicated that a piranha was getting pretty ticked off as it chased a competitor.

The first two sounds are produced by muscles contracting around the fish’s swim bladder. The findings are in the Journal of Experimental Biology. [Sandie Millot, Pierre Vandewalle and Eric Parmentier, "Sound production in red-bellied piranhas (Pygocentrus nattereri, Kner): an acoustical, behavioural and morphofunctional study"; Piranha audio courtesy of Sandie Millot]

The researchers are now interested in whether piranhas vocalize during mating. But they’ll have to travel to Brazil to study this in the wild—turns out that when it comes to mating in captivity, piranhas say, "no tanks."

—Cynthia Graber

[The above text is a transcript of this podcast.]