Nemo's Secret: Clownfish Use "Snappy" Trick to Make Weird Sounds

John Roach
for National Geographic News

May 17, 2007

Movie magic gave a human voice to the hero of Finding Nemo. Now scientists have figured out how real-life clownfish make "chirp" and "pop" noises to woo mates and ward off enemies.

The mechanism hinges on a pair of tendons apparently unique to the family of fish that includes clownfish, explained Michael Fine, a biologist at Virginia Commonwealth University.

The fish open their mouths by lifting their heads and lowering an apparatus that holds the tongue. The mouth opening then stretches the tendons to what amounts to a snapping point.

"The tendons connect to the lower jaw, and they cause it to slam shut," Fine said.

"And so basically what it's doing is clacking the teeth and mouth together. That's the first part of the sound."

"And we assume then that the vibration—this is the part we don't really understand—is exciting some other structure, presumably the jawbone," he added.

High-Speed Imagery

Fine is a co-author of a study on the sound-producing mechanism reported tomorrow in the journal Science. Eric Parmentier of the University of Liège in Belgium led the research.

The team used a combination of sound recordings with high-speed video and x-rays to observe how the fish moved when making the sound.

David Mann is a marine scientist at the University of South Florida who is an expert on fish sound production. He was not a part of the research team.

He said the paper and accompanying video describing the mechanism is "very convincing."

"It's pretty unique, and it's looking in a place where most of us haven't looked before, which is why it remained unknown for so long," he added.

Clownfish sounds were first recorded in 1930, but how the sounds were made remained elusive until now.

While lots of fish make noise, most do so using muscles attached to their swim bladders.

(Related: "Herring Break Wind to Communicate, Study Suggests" [November 10, 2003].)

Fine said the clownfish sound-making mechanism is a so-called exaptation, an adaptation that changes function.

"We know very little about the evolution of sound production in fish," he said.

"Here we have a system that is presumably part of a feeding mechanism … that was co-opted to being a sound-producing mechanism. It shifted from one function to another."

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