Piranha fish have at least three different sounds they make when they are angry or feeling threatened or aggressive, researchers found.

To figure out what sounds the feisty fishes made when feeling territorial, researchers at Belgium's University of Liège put a hydrophone in a fish tank containing red-bellied piranhas, which are native to South American rivers and harmful to humans.

We knew piranhas were able to make sounds but were not satisfied with the explanation for how they do it, University of Liege biologist Eric Parmentier said, National Geographic reported. We wanted to know how they do this and what these sounds might mean to other fish. 

They published their findings in The Journal of Experimental Biology. 

Piranhas are known to be sound-producing animals, they wrote in the study's abstract. Nevertheless, the biological significance of piranha calls remains unclear because sounds have been recorded only when specimens were held by hand or trapped in a gill net. 

A video provided by lead author Sandie Millot played the three sounds made by the fish while in the tank and suggested what each one could mean.

Researchers described one of the sounds as a repetitive grunt and suggested it could be the piranha's way of telling others to get away from them.

Another sound was described as a low thud and possibly meant the fish wanted to fight, researchers said.

Gnashing teeth comprised the third sound and corresponded to chasing behavior, according to researchers.

The nature of these fishes are quite special, and I suspect they can make more than three sounds, Parmentier said, National Geographic reported.

The experiment was not hazard-free.

We both visited the hospital because we were bitten and Sandie's finger was nearly cut in half, Parmentier said of himself and Millot, the Web site LiveScience reported.

Video courtesy of National Geographic