My Fish Has Its Mouth Wide Open – Do Fish Yawn?

You might have seen the fish in your tank opening their mouth wide open for a few seconds. It resembles a human yawn, but do fish actually yawn? What is yawning in the first place?

No, fish cannot yawn. We cannot term the opening of the mouth as yawning. Then what is it? It usually is a response to stimuli dependent on the situation or environment.

Well, if you are confused about this behavior of your pet fish, then you have come to the right place. In this article, we will discuss why fish open their wide open, do they feel sleepy, can they yawn, and other related stuff.

So, let’s begin without further ado.

Do Fish Yawn?

As mentioned earlier, fish cannot yawn.

Yawning is a way in which the mammals feel fewer fatigues and cool down their brain. While yawning, the temperate gets regulated, and as a result, we feel less tired.

However, in the case of fish, it is not the case. Fish are cold-blooded creatures, so they have absolutely no need for cooling their brain down. Moreover, they don’t sleep at all; they just rest. If you see a fish lying motionless in the corner of the tank, it is probably just collecting the energy by resting.

They just open their mouths which can seem like yawning, but it is not. It is mostly buccal pumping. What is buccal pumping? Well, it is when fish open their mouths to flush water through their gills.

You can see almost every fish like betta, puffer, goldfish opening their mouths wide open or, if you like to call it, yawning.

There can be many other reasons behind a fish opening their mouth wide open, which we will be discussing shortly.

Why is My Fish Opening Its Mouth?

The reasons behind your fish opening its mouth for a few secs can be many. Few reasons can be worth your worry as well. We have listed all the plausible reasons here for your reference. Have a look-

Gill Flushing

As mentioned before, fish open their mouths to flush their gills with water.

Water passes through the gills and is absorbed by the fish. As a result, they must open their mouths and swim to improve their oxygen saturation.

Little undesirable particles might become stuck to their gills when water passes past the gills. It can obstruct a smooth gas exchange and make breathing difficult for fish.

Therefore, the fish will open their mouth wide to clean their gills, allowing water to enter and exit through their gills. It flushes out all of the undesirable particles, allowing the fish to breathe normally.

A Reaction to Threat or Sexual Stimuli

Female fish tend to “yawn” to attract males by creating sounds with their mouths. It is a way to direct the male towards them.

Moreover, when fish confront an intruder, a fish will also expand its jaws wide. They do it to project authority over their territories.

Filter Feeding

Filter feeding is the phenomenon in which a fish filters out small food particles from the eater and consumes them. All the fish do this, right from the bony ones to the cartilage ones.

As you know, food gets mixed up with water sooner or later. You might not be able to see it, but there are some little particles of fish food floating in the tank most of the time.

So, the fish open their mouth and allow the water to enter their mouth, and they start filtering the food particles.

Lack of Oxygen in the Tank

If you notice your fish opening its mouth frequently, then it might be an alarming sign. It might mean that the oxygen levels of the water in the fish tank are poor. They will open and close their mouth restlessly to have more oxygen supply.

Immediately check the oxygen levels in the tank and adjust them accordingly.

Overcrowded Tank

If you put too many fish in the same tank, there can be a problem. Overpopulation means more consumption of oxygen, and there might be a point where oxygen levels fall considerably.

Moreover, overpopulation can also become the reason behind increased stress. Therefore, you should make sure that the tank has an optimum number of fish.

High Nitrate Levels

Excessive old food, plants, and fish waste can increase the nitrate levels in the fish tank’s water. Nitrates are very harmful to the fish and act as toxins if they are present in considerable amounts.

Breathing becomes difficult for fish in the presence of excessive nitrates, and as a result, they will open their mouths to increase their oxygen levels.

Fish Yawning – Good or Bad?

Fish yawning can be both good and bad. If they are opening the mouth in defense, it is fine. However, if they restlessly keep opening their mouth or yawn, they probably need help.

Clean the tank and check the oxygen levels to help your fish.


Fish do not yawn; they cannot. So now, if you see any fish opening its mouth wide open, look for possible causes. If it is something that you should worry about, take action immediately.