Clever Trout Match Chimps in a Cognitive Challenge


Certain forms of collaboration are supposed to be so sophisticated that only the smartest creatures—namely humans and perhaps a few close relatives—are capable of them. Yet this exclusive club has a new and unexpected member: a species of fish, a class of animals seldom associated with high-level intelligence.

As demonstrated in a series of experiments published today in Current Biology, coral trout not only solicit the help of moray eels when they hunt, but also pick their hunting partners wisely. They know when they need help, and quickly learn which eels best provide it. It’s a seemingly simple yet surprisingly sophisticated cognitive trick.

“Prior to our study, chimpanzees and humans were the only species known to possess both of these abilities,” said zoologist Alex Vail of England’s University of Cambridge. “I think the evidence is mounting that fish have more going on in their heads in terms of cognition than they have been given credit for.”

In earlier research, Vail and colleagues observed that coral groupers and coral trout—two closely-related species of large, reef-dwelling predatory fish found in the Indian and western Pacific oceans—used their bodies to point moray eels at prey hiding in otherwise inaccessible seabed holes. The eels followed directions, flushing prey from the holes and giving groupers an easy meal.

In the cognitive argot, this appeared to be evidence of referential communication: groupers didn’t merely express an emotional state or some straightforward want, as with a mating display. Rather, their gestures referred to an external object, and seemed to display conscious intent. It was not the behavior of a stimulus-response machine.

It was an exciting finding. In recent years, even as scientific journals burst with studies of clever crows and empathic rats and tool-using dolphins, fish remained at the back of the class. Yet that may say more about our own assumptions than anything else. Fish have been around for more than 500 million years, and have as much evolutionary incentive as other creatures to smarten up.

In the new study, Vail and his colleagues, fellow Cambridge zoologist Andrea Manica and biologist Redouan Bshary of Switzerland’s University of Neuchatel, decided to give coral trout an especially challenging test, adapting an experiment originally conducted with chimpanzees.

That experiment, published to widespread scientific acclaim in 2006, involved one chimp freeing another from a cage in order to jointly tug on a rope, thus releasing food that couldn’t be reached by a single chimp’s efforts. Chimps figured out when they needed help and learned which other chimps best provided it—aptitudes that until then had been considered uniquely human.

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