A person signing the word “fish” waves his or her hand back and forth to imitate a fish swimming. It turns out that two types of fish — grouper and coral trout — also use a kind of sign language called “referential gestures” when hunting. Both fish are known for hunting cooperatively — grouper hunt with giant moray eels and Napoleon wrasse, and coral trout partner with octopuses. A recent study found that the fish “point” their heads toward prey, a signal to their hunting buddies.
Researchers discovered that when prey escapes a grouper, the fish will occasionally move over the hiding place of the fugitive. The grouper then rotates so its head faces downward, and shakes it back and forth in the direction of the potential meal in what researchers call a “headstand” signal. Coral trout make a similar sign. That’s when the hunting-party buddies move in.
A moray eel can slide into crevices where small fish lurk, and the wrasse uses its powerful extendable jaw to suck out its prey from a hole, giving the grouper a chance to catch it. Coral trout similarly collaborate with octopuses, which can also fit into tight spaces. Teamwork ends once the prey is flushed, however — dinner goes to the fastest fins.