If you think that fish speak just in cartoons, well….you're wrong!

Researchers detected how clownfish - exactly the species depicted as Nemo - employ sound communication. By employing high-speed video imaging and X-ray technology, researchers discovered how fish use their jaws to emit warning sounds before expelling intruders from their territory.

This is the first time when a fish species was found to use its jaws to produce communication sounds.

Clownfish inhabit coral reefs in connection with some extremely poisonous animals, sea anemones (the fish being immune to their venom) which, using their venom, defend the fish against predators. Each clownfish is extremely territorial, defending its anemone or anemone side.

80 years ago, the researchers found how clownfish could emit a swift succession of clacking noises when they detect an intruder in their territory or want to show off for a potential mate. "It is like someone knocking on a door," describes Eric Parmentier at the University of Liege in Belgium, a fish ethologist. The clicks have a frequency of five sounds per second, but scientists were puzzled by how the fish produced them.

The high-speed video analyzing the clowinfish's (Amphiprion clarkii) movements, made Parmentier's team suspect that the fish employed the jaws to do that. The check if that is true, they inserted 1-2 mm metal pieces into the fish's jaw bones and tracked them with X-ray technology.

It clearly appeared that in one swift move, the clownfish pulls in a tongue-like structure, tugging on the upper and lower jaws, snapping them shut. The resulting knocking sound resembles our "chattering" teeth when we shiver. "Most people are not aware that fish are able to make sounds," says Parmentier.

If the intruder does not consider its warning calls, the resident clownfish will attack it. "This is the first time an animal has been shown to communicate by snapping the jaws in their mouth", he added.

Other fish employ bones from the back of their mouth to produce noises and some species communicate by releasing air out of sacs positioned near their intestines.