Damselfish release chemical signals to escape predators

Damselfish release a chemical 'distress call' when caught by a predator that attracts additional predators to the site which gives the fish time to flee, according to a new study.
The chemical 'distress call' can dramatically boost the damselfish's chances of survival, said researchers at the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University.
The chemical released attracts other predators to the site who attempt to steal the prey, giving the fish a chance to escape during the ensuing commotion.
Fish harbour a chemical substance in their skin that is released upon injury. It triggers fearful and escape behaviour in nearby fish, but until now scientists had not identified the benefits to the sender.

"For decades scientists have debated the evolutionary origin of chemical alarm cues in fish," said lead author Oona Lonnstedt, now a research fellow at the University of Uppsala.
The researchers have now found the answer after they studied damselfish (Pomacentridae) - a small, tropical marine species - and discovered that the chemical cue attracts additional predators to the capture site.

"Chemical alarm cues in fish seem to function in a similar way to the distress calls emitted by many birds and mammals following capture," said study co-author Mark McCormick from the Coral CoE.
"When damselfish release their chemical alarm on a coral reef, lots of additional predators are attracted to the cue release area," said McCormick.

"More predators would seem to mean more trouble, but we discovered that additional predators interfere with the initial predation event, allowing the prey a greater chance to escape," he said.
The research team found the new predators would attempt to steal the prey, and in the ensuing commotion the captured damselfish had a greater chance to break free and hide.
"When caught by a predator, small damselfish have almost no chance of escaping their fate as the predator's next meal," said McCormick.
"However, when another fish predator is attracted to the capture site, prey will escape about 40 per cent of the time," said McCormick.

Lonnstedt added that this proves that chemical alarm cues benefit the sender by giving it a much greater chance of not ending up as dinner.
"These findings are the first to demonstrate an evolutionary mechanism by which fish may benefit from the production and release of chemical alarm cues, and highlight the complex and important role chemical cues play in predator-prey interactions on coral reefs," Lonnstedt said.
"It all goes to show that coral reef fish have evolved quite a range of clever strategies for survival which are deployed when a threatening situation demands," she said.
The study was published in the Proceedings of the Royal Society B.