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Fish of two different species have been filmed helping each other to hunt. It is the first known instance of two unrelated species hunting cooperatively, except for humans. Like a hunter bringing a dog to flush out rabbits, groupers entice moray eels to hunt with them. Surprisingly, this might also shed light on how our own species evolved.

Groupers are bulky fish that hunt in daytime in the open water off coral reefs. Moray eels hunt by slithering through the reef at night. When both hunt together, prey barely stands a chance: hide in the reef, the eel eats you; dash for open water, the grouper grabs you.

Groupers appear to have worked this out or at least learned by association that hunting around eels is a good idea. Working in the Red Sea, Redouan Bshary of the University of Neuchatel in Switzerland, and colleagues watched groupers – especially hungry ones whose prey had just escaped into a crack in the reef – swim over to the nearest moray as it lays in its daytime hiding place, and perform a strange head-shaking dance, waving its dorsal fin.

Most of the time, the eel responded by following the grouper, which repeated the dance more slowly over the crevice where prey was hiding. The eel moved in for the kill – but flushed out other prey for the grouper.

On average, the researchers reckon both fish were five times more successful at catching prey together than separately.

The evolution of this cooperation between mammals is usually prevented because of competition for a single prey. But crucially, these fish swallow their prey whole, so there is no fighting over the spoils, say the researchers.

Groupers have also been observed hunting prey simultaneously with Napolean wrasse, Cheilinus undulatus.

Fulfilling a similar role to the moray eel, the wrasse cannot enter crevices where prey is hiding, but uses its jaws to destroy the hiding place instead.

These findings have some bearing on our own species. Some scientists think the cognitive skill needed for cooperative hunting is one of the reasons that humans evolved intelligence. Yet these observations, say the researchers, show you do not have to be any smarter than a fish to work out how to hunt with a friend.

Source: NewScientist.com by Debora MacKenzie on 5 December 2006
Journal reference: Public Library of Science (DOI: 10.1371/journal.pbio.0040431)