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Tiny Fish Grow Larger Fake "Eyes" to Distract Predators

Aug 19, 2013 05:46 PM EDT

The tiny damsel fish, frequent prey to larger fish and marine animals, has been found to increase the dark spot on its tail to appear to be a bigger "eye" while simultaneously shrinking the size of its real eyes.

Researchers report this tactic distracts predators and dramatically increases the damsel fish's chance of survival in the wild. By shrinking the size of its real eyes and increasing the "eye" on the back of its tail, the damsel fish is able to confuse predators and trick them into thinking the fish is traveling in the opposite direction.

"It's an amazing feat of cunning for a tiny fish," said Oona Lönnstedt, a graduate student at Australia's ARC Centre of Excellence for Coral Reef Studies (CoECRS) and James Cook University.

"Young damsel fish are pale yellow in color and have this distinctive black circular 'eye' marking towards their tail, which fades as they mature. We figured it must serve an important purpose when they are young."

For years aquatic researchers have been puzzling over whether the false eyespots on less vulnerable parts of fish played a role in protecting them from predators or if it was the result of a fortuitous but accidental evolutionary quirk.

The CoECRS team reports its find to be the first clear evidence of a fish changing the size of its real eyes and and its misleading eyespot to maximize survival chances when under threat.

"We found that when young damsel fish were placed in a specially built tank where they could see and smell predatory fish without being attacked, they automatically began to grow a bigger eye spot, and their real eye became relatively smaller, compared with damsels exposed only to herbivorous fish, or isolated ones," Lönnstedt said.

"We believe this is the first study to document predator-induced changes in the size of eyes and eye-spots in prey animals," she added.

When the researchers observed the fish in the wild, they documented a survival rate five time higher for fish who grew their tailfin "eyes" compared to fish that did not.

"This was dramatic proof that eyespots work -- and give young fish a hugely increased chance of not being eaten," Lönnstedt said.

She added: "We think the eyespots not only cause the predator to attack the wrong end of the fish, enabling it to escape by accelerating in the opposite direction, but also reduce the risk of fatal injury to the head."

Lönnstedt and her colleagues' research is published in the journal Scientific Reports.

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