Watch: Fish and Eels Team Up to Catch Prey—Rare Among Animals

Talk about lending a helping “fin”—groupers and eels in a coral reef work together to catch prey, a new study says.

Previously, scientists had thought only humans and chimpanzees collaborated in this way, suggesting that teamwork may be more widespread in the animal kingdom than thought. (Also see “Groupers Use Gestures to Recruit Morays For Hunting Team-Ups.”)

When prey is out of reach in a crevasse in the western Pacific Ocean, the big, red grouper—actually called a coral trout—will shimmy back and forth in front of a moray eel, essentially “asking” the moray eel for help in flushing out its victim. (Also see “Fish ‘Engineers’ Dig Up Homes for Marine Life.”)

Though shimmying conveys “let’s go hunting” in aquatic sign language, not all moray eels are created equal. The research, published September 8 in Current Biology, shows that coral trout are able to learn and remember which individual moray eel is best for the job and return to that one again and again. In return, the moray eel gets to eat whatever the coral trout can’t catch.

“This study makes us take a step back and think about how the cooperative behavior we’ve seen in chimpanzees doesn’t just exist because they are so similar to [humans],” said David Steen, a wildlife ecologist at Auburn University in Alabama who was not involved with the study.

“Perhaps we should acknowledge that a wide variety of animals can engage in exciting and advanced behaviors that we previously had thought helped distinguish us,” he said by email.

Go Fish

For the experiment, scientists at the University of Cambridge in England and the University of Neuchâtel in Switzerland re-created a typical hunting scenario in the lab with captive coral trout.

The researchers made two puppet moray eels, one of which was deemed helpful and the other unhelpful.

When the coral trout visited the unhelpful “moray eel” and did their shimmies, the scientists-turned-puppet-masters had the moray swim in the wrong direction. However, when the fish approached the helpful moray, it would effectively do its job, and the fish was rewarded with dinner. (Also see “Pictures: Sharks Taught to Hunt Alien Lionfish.”)

After 48 trials over the course of six days, the coral trout learned which moray eel could help it achieve its goals, and would enlist that moray’s assistance, said study leader Alex Vail, a marine biologist at Cambridge.

Brain Power

The study is an advance, but it brings up a lot more questions than it answers, said Tom Kwak, a fisheries ecologist at the U.S. Geological Survey’s North Carolina Cooperative Fish and Wildlife Research Unit who wasn’t involved in the research.

For instance, the next step is to explain how the fish are able to carry out these complicated tasks with such limited processing power.

A photo of a coral grouper being cleaned by a shrimp.
A coral grouper (Plectropomus leopardus), also called a coral trout or leopard coral grouper, gets its mouth cleaned by a clear cleaner shrimp in the Maldives in 2009. Photograph by Jason Isley, Scubazoo/Science Faction/Corbis

A fish’s brain is much simpler than that of a chimp or person because it has far fewer nerve connections.

It’s possible that fish get around this limitation by using their brains very efficiently, but that’s unknown. (Read “Minds of Their Own” in National Geographic magazine.)

“[Humans] think about something we want and try a whole bunch of ways to achieve it. Do animals think it through or do they just do a behavior?

“We have to work out what kind of mental processes they use to do these collaborations.”

Whatever the mechanism, noted Culum Brown, a biologist at Macquarie University in Sydney, “fish are far smarter than most people give [them] credit [for].”

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Mollie Bloudoff-Indelicato is a science journalist who loves em dashes, ’80s music and parasites. She has a master’s degree from the Columbia University Graduate School of Journalism with concentrations in science journalism, photography, and radio reporting. Contact her at, and follow her on Twitter at @mbloudoff.