Fish Use Sign Language to “Talk” to Other Fish
Great apes and ravens have been known to use sign language. In a first, scientists from the University of Switzerland in Neuchatel in Switzerland and Cambridge University have found that a reef fish, the coral grouper, does too. Moreover, coral groupers use their communication skills to help other types of fish.
Coral groupers (Plectropomus pessuliferus marisrubri) are predator fishes who live in tropical reefs. They can be about three feet long and have previously been observed to have an “unusual relationship” with two other kinds of large fish, giant moray eels (Gymnothorax javanicus), who can be almost 10 feet long, and Napoleon or humphead wrasses (Chelinus undulatus). Male Napoleon wrasses grow to some six feet long and females up to three feet.
The scientists discovered that the three types of fish cooperate to hunt for food. Each contributes specific abilities: the grouper uses its “burst speed” to capture prey in the water. The eels are able to insert themselves into crevices where smaller fish are to be found. The wrasses use their powerful, and extendable, jaws to suck out prey in a hole or to simply smash the reef that a fish has taken refuge in.
In hunting, the grouper uses two “signs.” One is a “high frequency shimmy” that amounts to a shaking of its body; this is performed in front of a moray eel as a sort of “invitation” to join the chase for prey. The second gesture, a “headstand” — in which it positions itself vertically and with its head down — is “referential,” as the grouper uses it to indicate to its hunting companions where a smaller fish might be hiding, or where it was last seen.
Researchers observed these behaviors among the three types of fish in 187 hours of observation, in the waters of Egypt and the reefs in Australia. They found 34 instances of the grouper performing a headstand; in 31 of these instances, a moral or a wrasse quickly appeared to take a look at the location the grouper had indicated. Prey was captured in five instances.
The study reveals that it’s not only vertebrates with large brains who are able to communicate in signs that are directed to a specific recipient, responded to voluntarily and shown to have the “hallmarks of intentionality.” Some types of fish indeed have a specific “goal in mind” and seek to communicate it via gestures that are not at all involuntary:
Key evidence is that the grouper elaborates on its headstand signal when the moray eel does not react appropriately to its signal and swims over to the eel, tries a different signal and in some cases even tries to push the moray in the prey’s direction. The researchers also observed groupers waiting above a hidden prey for up to 25 minutes before signalling to a passing predatory partner. They say this suggests groupers may perform at an ape-like level in a memory task commonly used to assess cognitive ability.
“In the animal world, postures or referential gestures have until now only been seen among great apes and ravens,” comments Redouan Bshary of Neuchatel University.
Chimps, gorillas and orangutans have been taught to sign, with some learning more than 200 different signs. Ravens have been found to make “hand gestures” using their beaks and wings. When it comes to communication, we all do what we can to get our point across.
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