You know that feeling. You see someone yawn and all of a sudden you, too, feel the urge to yawn. It turns out that’s not unique to people, or even mammals. At least one type of fish will do this, too.

Contagious yawning has been witnessed in several warm-blooded creatures. Besides us, these include chimps, lions and wolves. But here “is the first time this has been demonstrated in [a cold-blooded] species,” says Elisabetta Palagi. She works at the University of Pisa in Italy. As a comparative ethologist, she studies the behaviors of animals, often in the wild. Much of her work has focused on contagious behaviors — including yawning — in primates, such as monkeys and apes.

In a new study, she and her team were curious to confirm whether fish yawn — and if it’s contagious in them, too. People with freshwater aquariums often keep zebrafish (Danio rerio). That’s the species Palagi’s team chose for this work.

The scientists started by observing and filming 18 zebrafish in the lab. The fish usually breathe by quickly opening and closing their mouths. But sometimes they opened their mouths slowly. They also stretched it widely — then snapped it closed. This seemed to mimic what scientists usually describe in other animals that are yawning (including us).

The researchers turned up many differences between a fish’s normal breathing and a yawn. For instance, the fish opened their mouth wider during a yawn than when simply breathing. And about half the time, a yawning fish also stretched its body. This is “very interesting,” Palagi says, and something “we absolutely did not expect to find.” (Yawning people also tend to stretch their bodies about half of the time, she notes.)

Palagi and her team then trained an AI model to recognize those traits they had linked to yawning. Afterward, the researchers gave the AI many screenshots taken from videos of fish. In short order, that AI could distinguish between a yawn and normal breathing, in much the same way her group did.

Next, the researchers showed zebrafish two types of videos. In one, a zebrafish yawned. In the other type, the fish just breathed normally. Palagi’s group showed these videos to many fish and many times to each individual. Then they analyzed how the creatures responded.

The fish were more than twice as likely to yawn when watching a video of another zebrafish yawning than when they were just breathing. This suggests yawning is contagious, the researchers now conclude.

Zebrafish tend to swim in large groups, moving fast and changing direction as one. In the lab, when a fish responded to the video of a yawn, it also tended to change the direction in which it was swimming. In the wild, such a directional change in response to yawning might help zebrafish coordinate their movements, the researchers suspect. 

Palagi’s team shared its findings April 7 in Communications Biology.

These data aren’t convincing everyone

“This reads to me like the beginning of something — but nothing massively conclusive,” says Cait Newport. She’s a biologist who studies fish behavior at Oxford University in England. She did not take part in the new study.

While she thinks these observations offer a “good start,” it’s still unclear why the fish would yawn together, she says. The directional change reported in fish that watched a video, she adds, is not enough to conclude that fish in the wild would use yawning to coordinate their movements. But it’s a plausible hypothesis, she says.

Noam Miller is a comparative psychologist. He works at Wilfrid Laurier University in Waterloo, Ontario, Canada. He finds the Italian group’s study “very interesting” and “surprising.” Still, he adds, there are many things left to learn.

“We’ve seen contagious yawning in a lot of mammals and birds — and then we have this one fish study,” says Miller. “We need to fill in a lot of these gaps” on whether fish would yawn — and do it contagiously — for the same reasons those warm-blooded animals do.

Why animals yawn is still an open question, Palagi says. But she and her team think zebrafish could be a perfect animal to study yawning and why it’s contagious. In fact, they plan to do just that. “This study opens the floodgates for many more [studies] to come.”