A study published in Nature demonstrates that fish have a natural rhythm that could help them avoid being eaten by predators

A team from the University of California led by Dr Mu-Ming Poo made the discovery during experiments with zebrafish, a type of minnow. They discovered that the larvae of the fish, which were trained to flip their tails every time a light flashed at six-second intervals, "remembered" the rhythm even after the flash was turned off.

The reason why the fish kept time was a mystery but it could be to help it keep track of time and defend itself.

"A predator of the zebrafish larva is the larva of the dragonfly," one of the co-authors Dr German Sumbre said. "This predator attacks the zebrafish and its success rate is very low, missing many times.

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Between attacks the dragonfly larva has to re-posture for the new location of the zebrafish larva, this may take a few seconds.

Therefore after a few attacks, the zebrafish larva may learn the "rhythm" of attacks, and thus be able to predict the next one. In this way, the larva can escape faster, even before the attack."