Scientists Discover That Certain Fish Use Sign Language When Hunting

Scientists have known for decades that primates such as gorillas and chimpanzees can learn and understand sign language and communicate with one another using gestures. More recently, ravens have been observed to show similar behaviors, but until now, scientists believed that those two types of animals were unique in their ability to do so. However, an article published recently in Nature Communications suggests that our understanding of animals’ ability to communicate through gestures is less complete than we may have believed. Certain fish are showing the ability to communicate with one another using body language in order to hunt more successfully in teams.

bass fishThe body language these fish use is called referential gesturing. Because scientists don’t know what the fish are thinking, it’s hard to prove that a given behavior is a referential gesture, but there are several criteria that scientists use to classify these behaviors as a form of communication. First, the behavior must be directed at an object (for example, the prey) and aimed at a recipient (another fish). The gesture must have no mechanical purpose (for example, swimming) and must appear to be voluntary and intentional. Finally, it must elicit a response from the recipient. The behaviors seen in two kinds of fish, the grouper and the coral trout, while hunting, fit all of these criteria and appear to be a form of sign language.

Grouper and coral trout are known to cooperate with other species of fish, such as octopi, moray eels, and wrasses, to hunt more effectively. Grouper and coral trout are fast swimmers in open water, while the other fish have the ability to navigate small spaces in coral to capture prey. Scientists have observed both grouper and coral trout to point out escaped prey in hiding spaces that they cannot reach. The grouper and coral trout will perform a “headstand” pose, tilting and pointing at the hidden prey. In many instances, the octopus, eel, or wrasse will respond by seeking out the prey in its hiding place and frequently capturing it. By communicating and hunting in teams, the fish are able to greatly increase the number of successful hunts, and all of the predators get a meal more often.

For many years, scientists believed that language and communication required a large amount of intelligence and brain capacity. However, it is clear that fish do not display the same level of intelligence as mammals or birds, and that they actually lack parts of the brain that mammals and birds use. This research may open doors for future study in language development. It appears that intelligence and brain size may be less important than evolutionary pressure for the development of communication behaviors. For the fish, the need to hunt in environments like the insides of reefs that are unsuited to the speedy grouper and coral trout resulted in pressure to develop a partnership with a more agile ally, and all partnerships work better when the partners are able to communicate with one another. Not only may the fish be more intelligent than we have ever given them credit for, but necessity may truly be the mother of invention even in the depths of the ocean.