Scientists have found that a group of reef fish called the roving coralgrouper uses sign language to tell fellow hunters where prey is hiding.
This is the first time a fish was known to use "referential gestures" to tell others where food was located.
The report was published in the journal Nature Communications by three biologists at Switzerland's University of Neuchatel and Cambridge University in England.
They found that there is a certain relationship between the coralgrouper, the giant moray eel and the Napoleon wrasse which involves communicating to each other about where prey is hiding.
The three species each have their own strengths which, when combined, enable them to capture prey easily. The eel is able to slide into small places where fish hide, the grouper is speedy in open water, and the wrasse has powerful jaws that can suck out prey from holes or smash reef surrounding it.
There are two signals the grouper uses to convey messages. The grouper's first move is a "high frequency shimmy," performed in front of a moray to invite it to join in on a hunt.
The second type of signal is a "referential," which is performed through a headstand. The headstand is pointed up or down, indicating to the moray or the wrasse where the prey was last seen.
Biologists observed 187 hours of the groupers in reefs off of Australia and Egypt. There were 34 recorded instances of the referential and 31 cases of either a moray or a wrasse rushing to inspect a location where the grouper pointed. Five of those cases ended up in the capture of prey.
"In the animal world, postures or referential gestures have until now only been seen among great apes and ravens," researcher Redouan Bshary said.