In a pack hunt, it’s every goatfish for itself

These fish hunt selfishly with a touch of accidental helpfulness

goatfish

SEL-FISH Pure self-interest could explain the smoothly coordinated moves and effective collaboration in hunting packs of yellow saddle goatfish.

M. Steinegger

The only fish known to hunt with wolf pack moves may not be true team players, just lemon-yellow me-firsts.

Yellow saddle goatfish (Parupeneus cyclostomus) do more than school together as they dart over Indo-Pacific coral reefs. Like wolves, the goatfish take different roles in a pursuit. One or two fish may rush straight toward prey as the others shoot to the sides, blocking escape.

“They look harmless, but they’re vicious predators,” says Redouan Bshary of the University of Neuchâtel in Switzerland. “That’s why it’s fun to follow them — there’s always action.”

He and his colleagues have documented other fishy hunting partnerships, such as groupers pairing with crevice-wriggling moray eels. Goatfish collaborate with their own species, though probably not their close kin, Bshary’s team has reported. The fish chase other small, fast reef fish, “a little bit like Ultimate Frisbee,” says Dominique Roche, in Bshary’s lab. “It’s a game of sprinting and stopping.” The bright yellow goatfish dart into a reef “like a lightning flash.”

BEWARE THE BARBELS Under the chin of a yellow saddle goatfish, two long skinny barbels can unfold and poke into sand or slide into a rubble crevice in search of prey. Albert Kok/Wikimedia Commons (CC BY-SA 3.0)
When wolves hunt together, some will take a risky role even though they won’t get a greater share of the reward, Roche says. A goatfish pack, however, doesn’t deal in heroics. In lab studies of them pursuing a treat on a string, any help a fish gives its comrades could be explained as an accidental by-product of self-interest , Bshary, Roche and colleague Marc Steinegger say in the Jan. 31 Proceedings of the Royal Society B.

In the tests, two goatfish swimming close to each other when the treat appeared usually shot after it together. If the two fish were more than a body length apart, however, the trailing fish typically darted to the side, where it might catch the frantic prey if it veers from the lead pursuer toward some shelter.

Those side moves are a lagging fish’s best chance for catching anything, Roche says. Watching goatfish in the Red Sea close in on some little fish, he typically sees them space themselves just about evenly around their prey. The simple rule of taking the best position considering the goatfish’s starting point could easily — and unintentionally — help a fellow hunter nab a meal.

CLOSING IN Three yellow saddle goatfish (with an onlooker) space themselves around prey that’s taken shelter. The hunters’ coordination here could be explained just by self-interest. M. Steinegger

Goatfish don’t share their small prey. But as the hunting party darts among the corals, collaborators come upon prey at different angles, boosting their chance of catching more together than they would alone.

“There was a strong belief for a long time,” Roche says, that for true collaborative hunting “you must need a really big brain to process complex information.” The test, he says, shows what can be done when a “small-brain fish” makes self-interested decisions.

Editor’s note: This story was updated March 7, 2018, to clarify that researchers predict that goatfish will catch more prey in a group hunt than alone, but the idea has not been shown yet.

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