Two types of fish have been shown to use gestures, or sign language, to help one another hunt. This is the first time these types of gestures have been found to occur in animals other than primates and ravens.
Both types of fish, grouper and coral trout, are known for hunting cooperatively with other kinds of animals. Whereas the grouper hunts with giant moray eels and a fish called the Napoleon wrasse, coral trout partner up with octopuses to snag prey. A study found that the fish are able to "point" their heads toward prey, to help out their hunting buddies.
After observing the fish in the wild researchers found that when a prey fish escaped its hunting party, a grouper occasionally moved over the place where the fugitive prey was hiding. The grouper would then rotate its body so that its head faced downward, and it would shake its head back and forth in the direction of the potential meal, in what researchers call a "headstand" signal. Coral trout make a similar sign.