Tiny Damsel Fish Distract Predators by Growing False Eyespot on Their Rear Fins

A team of Australian researchers discovered that the tiny damsel fish grow bigger eyes near their tail to distract predators and enhance their chances of survival.

The new scientific study conducted by researchers at Australia's ARC Centre of Excellence for Coral Reef Studies (CoECRS) reveals that the small damsel fish develop large false eyespots on their rear fins and also reduce the size of their real eyes. The tiny fish use this technique to confuse the predator by making the killer fish assume that the fish is heading in the opposite direction.

For years several experts have debated on whether false eyespots and circular marks found on the less vulnerable parts of  prey animals protect them from predators.

It is for the first time that the CoECRS research team has provided clear evidence of the role the  dark circular marks play. They said that the fish can alter the size of both the real eye and false eye spot to boost their chances of survival when they face constant threat from predatory fish.

"It's an amazing feat of cunning for a tiny fish. Young damsel fish are pale yellow in colour 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. 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 one," Oona Lonnstedt, a graduate student at CoECRS and James Cook University said in a news release.

The Damsel fish mainly dwell in the tropical coral reefs and usually have bright colors. They can grow up to 14 inches and feed on crustaceans, planktons and algae.

This is the first study that documented the predator induced changes in the size of real eye and false eye spots in prey animals. The researchers also discovered that the juvenile damsel fish that had enlarged eye spots had five times greater survival rate compared to the damsel fish with normal size spot.

The eye spots not only tricks the predator to attack the wrong end of the fish that gives an easy escape for the prey fish but also lowers the risk of fatal injury to the prey fish's head.

The prey fish also adopt different protective behavior such as lowering the activity levels, developing chunkier body shape making it difficult for the predator to swallow them and seeking shelter often.

The study "Predator-induced changes in the growth of eyes and false eyespots" is documented in the journal Scientific Reports.