Clown fish became famous thanks to the movie Finding Nemo. In real life, their social hierarchy is simple: larger fish dominate their smaller counterparts. Now we know that to reinforce this social structure, the fish communicate with aggressive and submissive audio signals. The new info is in the journal PLoS ONE. [Orphal Colleye and Eric Parmentier, Overview on the Diversity of Sounds Produced by Clown Fishes (Pomacentridae): Importance of Acoustic Signals in Their Peculiar Way of Life]
Researchers recorded clown fish calls, capturing this noise as one chased a smaller fish. [Aggressive audio] These popping sounds function as an aggression signal. When a clown fish has been chased and wishes to submit, it shakes its head in a submissive gesture and produces clicking noises like these. [Submissive audio] The researchers compared the aggressive and submissive calls, and found that the sound pulses in a submissive signal were shorter and more high-pitched.
Unlike many animals that use sound to draw in potential mates, clown fish appear to use their calls only as labels of social status. When a little fish makes submissive sounds to a larger one, neither has to invest in a physical confrontation. Which is good news for small-fry like Nemo.
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