Got Rhythm? Baby Zebrafish Do

Rebecca Carroll
for National Geographic News
October 15, 2008

Zebrafish babies got rhythm—and shake their booties to prove it, a new study shows.

After being "taught" a rhythm using flashes of light, the larvae "remembered" the beat pattern for 20 seconds after the flashes ceased, scientists found.

The finding, published online Wednesday by the journal Nature, suggests that the fish possess a sort of mental metronome that can help them elude predators.

With each light "beat," the baby zebrafish wiggled their tails and experienced activity in the sections of their brains that process visual information, the optic tectum.

When the researchers turned off the lights, the fish continued to wag their rears and show signs of brain activity in time with the rhythm.

"The activity may represent expectation, so to speak," said study co-author Germán Sumbre, who led the research at the University of California, Berkeley's Poo Lab and now is a researcher at the École Normale Supérieure in Paris.

By anticipating the next beat, the fish might be better able to react to predators, said Sumbre.

(Read about animal minds.)

Aerial Evasion

Dragonfly larvae are the chief predators of zebrafish babies, and the fly larvae's attacks may be somewhat rhythmic.

"They are not very good at capturing the zebrafish larvae," Sumbre said. "The literature suggests their success rates are very low and it takes a few seconds to rearrange their orientation before they attack again."

By "learning" the dragonflies' rhythms, the fish may anticipate their enemies' next moves, thus "escaping in a better or faster way," said Sumbre.

Good Memories

Similar neural responses to rhythm have been seen in fish before, but not for a period as long as 20 seconds.

Catalin Buhusi, a neuroscientist at the Medical University of South Carolina who was not involved with the study, said the research uses interesting methods, but that the 20-second retention may not technically be memory.

Buhusi noted that pendulums continue to sway rhythmically for a limited time on their own after they've been set in motion.

"You can learn that something important happens every ten seconds," Buhusi said. "I think it's a basic form of attention."

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