Damselfish Escape Predators With Chemical Distress Alarm, Researchers Say

When they're captured or injured, some damselfish (Pomacentridae) release a chemical distress alarm that ultimately confuses large predators and buys the fish time to flee, researchers from James Cook University revealed in a new study. This signal sends surrounding fish into defense mode and greatly improves their chances of survival. Until now, researchers were unsure how this chemical distress call benefits the sender.  

"Chemical alarm cues in fish seem to function in a similar way to the distress calls emitted by many birds and mammals following capture," Professor Mark McCormick, study co-author from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University, said in a news release.

Damselfish are relatively small fish that only grow to be about 14 inches long. Generally, most damselfish are dressed in brightly colored scales and live along tropical coral reefs. They prefer to feed on small crustaceans, plankton and algae. 

"When damselfish release their chemical alarm on a coral reef, lots of additional predators are attracted to the cue release area. 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," McCormick added.

As predators, such as the Dusky Dottyback (Pseudochromis fuscus), compete to steal a captured damselfish, chaos ensues and their prey has a greater chance of breaking free and finding a safe hiding spot before the larger predators even realize what they are fighting over has escaped.

Researchers studied this behavior along the northern Great Barrier Reef, Australia, throughout the months of October to December in 2011 and 2012. They found that when the damselfish released its chemical distress call the fish were able to escape about 40 percent of the time. 

"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." Dr. Oona Lönnstedt, lead author of the study and now a research fellow at the University of Uppsala, said in a statement. "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."

The study was recently published in the journal Proceedings of the Royal Society B.

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