Study: Reef fish grow 'eyes' on their tails to escape predators

TOWNSVILLE, Australia, Aug. 19 (UPI) -- Small prey fish can grow a bigger "eye" spot on their rear fins -- and reduce the size of their real eyes -- to escape predators, Australian researchers say.

Scientists at the ARC Center of Excellence for Coral Reef Studies have found that small damselfish not only grow a larger false "eye spot" near their tail but also reduce the size of their real eyes.

The result is the damselfish looks like it is heading in the opposite direction, potentially confusing predatory fish, researcher Oona Lonnstedt said.

"It's an amazing feat of cunning for a tiny fish," Lonnstedt said. "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."

On natural coral reefs, the researchers found, juvenile damselfish with enlarged eye spots had five times the survival rate of fish with a normal spot.

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

The phenomenon was also studied in a laboratory setting.

"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," Lonnstedt said, "and their real eye became relatively smaller, compared with damsels exposed only to herbivorous fish, or isolated ones."

"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."