This is 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 under water 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 hunk.

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.

And he found that he could actually differentiate individual piranha species by analyzing factors

like pitch and harmonics and number of barks. His colleague Francis Wannes presented the work

at the Acoustical Society of America meeting in Victoria, Canada. Roundtree also recorded

10 hours of underwater soundscapes, like this one, captured during a

piranha feeding frenzy.

There's a piranha honk, he says, and lots of catfish screeching, which suggests that with a bit more study,

...