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Do fish yawn? And what is yawning in the first place?

Everybody yawns once in a while. In fact, there is a huge chance that you are going to yawn while reading this article. Just seeing the word “yawn” may make you yawn. People yawn, dogs yawn, snakes yawn, but do fishes yawn? And why do we yawn in the first place?

Yawning in the painting by Edgar Degas. Image credit: Edgar Degas via Wikimedia

Actually, the last question is a bit complicated – we don’t know why we yawn. For the longest time scientists thought that this reflex is meant to increase oxygen saturation in our blood. And it does do that a tiny little bit, but at this point scientists pretty much rejected this hypothesis. Nowadays it is believed that yawning helps too cool mammalian brain. However, we do know that some geckos and even snakes yawn as well, but do fish?

What is a yawn? It is a reflex of inhaling a lot of air and stretching eardrums at the same time. We do accompany it with some good old stretching, but that is not a part of yawning, really. That is why we do not know if snakes yawn – we don’t know if they are inhaling air deeply like we do or are they just stretching their jaw. It is a very similar story with fish.

Stickleback fish open their mouths sometimes very wide and move their bodies in a way that looks like stretching. Meanwhile  Siamese fighting fish seems to be yawning upon seeing another fish, sometimes even of its own species. However, then it jumps into an aggressive attack, which kind of shows that it is not really yawning, even if it looks like that for us.

Siamese fighting fish may look like they are yawning, but they are actually just warning their competitors about an incoming attack. Image credit: Daniella Vereeken via Wikimedia (CC BY 2.0)

Fish do not yawn, at least not the way we do. They do open their mouths sometimes, but that is typically to attract mates or deter aggressors. They do not breath in the same way we do, since they do not live in an environment of air. Water passes through gills, allowing the fish to absorb it. This means that they need to open their mouths and swim in order to increase their oxygen saturation.

We always attribute our own behavioural traits to animals. They may not be smiling, even if it looks like they are. They may not be ashamed or feel guilt after doing something bad – eyes pointing down may be a sign of fear. They may not be crying in the same way we do either.

Baboons yawn like us, but they also yawn to show their aggression. Image credit: Bjørn Christian Tørrissen via Wikimedia (CC BY-SA 3.0)

For example,  baboons yawn to threaten their enemies by displaying large canine teeth. But is it a yawn? Maybe visually, but the purpose and mechanics of this action is not the same.

However, many animals do yawn. Horses, cows, cats and other mammals definitely do yawn. For example, dogs sometimes start yawning after seeing their owners yawn. And it’s cute. But fish do not yawn.


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