Lionfish may be surprisingly sophisticated at hunting with partners. They shimmy their tails and fan out their fins in a signal that recruits a buddy, and they might even take turns gulping prey.
Divers have reported venomous, leafy-looking lionfish seeming to work together while corralling littler fish. But behavioral ecologist Oona Lönnstedt says that she and her colleagues are the first to test the behavior experimentally.
In a lab setup, Dendrochirus zebra lionfish from Australia’s Great Barrier Reef reacted to the sight of prey by swimming away and approaching another lionfish, which was caged and couldn’t see the prey fish. Hovering just in front of the second fish, the one that had seen the prey performed a distinctive sequence of gestures as if to say, “C’mon! Let’s go get ’em.” When researchers loosed the two lionfish on the prey, each attacker caught a bigger dinner than a typical lionfish hunting alone.
And the lionfish didn’t fight over this bounty, instead striking one at a time, Lönnstedt of James Cook University in Townsville, Australia and her colleagues report June 25 in Biology Letters.
The study adds to growing evidence“that fish social behavior is much more complex than previously assumed,” says Redouan Bshary of the University of Neuchâtel in Switzerland.
Fish don’t often get credit for having the smarts needed for cooperation, Lönnstedt says. Yet a report from more than 20 years ago indicated that a different lionfish species teamed up to corner smaller fish. And Bshary and his colleagues have proposed that roving coralgroupers produce a communication signal that draws a partner into a hunt: The coralgroupers frenetically shake their heads in front of giant moray eels’ hideouts and start a two-species joint hunting expedition.
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Lönnstedt and her colleagues now propose that the D. zebra lionfish likewise enlists a hunting buddy. She noticed partnerships as well as an unusual string of gestures as she swam around the reefs.
She allowed a lionfish to explore a lab setup and then added six little fish to a compartment for prey. The lionfish typically swam away from the prey and displayed what Lönnstedt thinks is a signal to kick off a hunt. The signaler faced downward and undulated its tail, as it often does when hunting, and then spread out and waved one pectoral fin and then the other. D. zebra lionfish performed the routine for potential partners of its own species and for another lionfish species familiar from its home reefs. Lönnstedt never saw the display without prey or a potential partner in the arena, she says.
When she allowed the lionfish to hunt together in the test arena, eight times out of 10, the fish that had initiated the display took the first strike and then backed off as the second fish rushed in. A lionfish doesn’t back off because it needs time for dinner to slide down the gullet, Lönnstedt says. When feeding alone, lionfish swallow prey fast. Instead, she says, the hunters in pairs “seemed to be almost polite.”
This possible turn-taking is something Bshary hopes the researchers will explore further. He muses over possible explanations to test: For example, the first strike could drive prey into new positions, so that a neighbor gains the best angle. The most remarkable reason would be that this behavior really is tit-for-tat cooperation that evolved as a trade of favors. That would really shake up old prejudices about the mental powers of fish.