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This is Scientific American's 60-second science. I'm Christopher in Taliatta.

Six years ago, the fish ecologist Rodney Roundtree was on a skiff in the Peruvian Amazon.

He was holding a piranha in his hand, underwater in a river filled with other piranhas, maybe hungry ones.

That thought crossed my mind a little bit.

The water was essentially no visibility.

So I did worry a little bit about that, but there was no other way to do it.

The job he needed to do?

Audition them for sound production.

Because Roundtree studies the sounds fish make.

His nickname and the name of his

company. The fish listener. So his team would catch a fish, reel it in, and identify it. And then

Roundtree would hold it underwater near a hydrophone to capture the sounds it made, like this one from a

red piranha. A lot of people call it a bark.

I sometimes thought of it as a honk.

The fish make the sound, he says, by pushing and pulling on their swim bladder with the

surrounding muscles.

Overall, Roundtree auditioned 129 piranhas of four different species, along with dozens of other river species, like catfish.

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