From: Debra Goldberg, ENN
Published August 19, 2013 10:01 AM

Small Fish Develop Disguises for Survival

A recent study, performed by researchers from Australia’s ARC Center of Excellence for Coral Reef Studies (CoECRS) and James Cook University, reveals that particular tiny fish have developed deceiving behaviors and features to enhance their survival chances against predatory fish. The damselfish, a tiny yellow fish with an eyespot on its tail, is capable of changing the size of its actual eye and eyespot in order to confuse and distract larger predators. This is the first study to document predator-induced changes in the size of eyes and eyespots in prey fish.

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Graduate student at CoECRS and James Cook University, Oona Lönnstedt, found that the eyespot causes the fish to appear to be heading in the opposite direction, potentially confusing predatory fish. A study performed on a natural coral reef with many predators showed that juvenile damselfish with larger eyes spots had survival rates five times greater than fish with normal-sized spots. According to Lönnstedt, "this was dramatic proof that eyespots work — and give young fish a hugely increased chance of not being eaten. 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."

When placed in a control tank where they could see and smell predatory fish without being attacked, juvenile damselfish automatically began to grow bigger eyespots. Additionally, their real eyes became smaller as their spots grew, when compared to damselfish exposed only to herbivorous or isolated fish.

"It all goes to show that even a very young, tiny fish a few millimeters long have evolved quite a range of clever strategies for survival, which they can deploy when a threatening situation demands," says Lönnstedt. It was also noted that young damselfish adopted other protective behaviors such as reducing activity levels, taking refuge more often, and developing a chunkier body shape, which made it harder for predators to swallow.

"It’s an amazing feat of cunning for a tiny fish," declared Ms. Lönnstedt.

Their paper, "Predator-induced changes in the growth of eyes and false eyespots" by Oona M. Lönnstedt, Mark I. McCormick, and Douglas P. Chivers appears in the latest issue of the journal Scientific Report.

Read more at ARC Center of Excellence - Coral Reef Studies.

Damselfish image via Shutterstock. 

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