How do fish sleep?

The sleep is vital for humans. Without sleep, significant changes in consciousness would occur within a few days, which in the worst case could lead to death .

Sleep is also a source of relaxation for animals. With dogs, for example, you can observe that they kick their legs wildly or bark loudly. Similar to humans, they process what they have experienced in their sleep.

Fish are special in this regard. From the outside it is hardly recognizable whether the aquarium inhabitants are sleeping or are wide awake. However, there are signs of the resting phase and it has also been confirmed that fish are asleep. How do you recognize the fish’s sleep and what characterizes it?

Outwardly, fish are very different from other animals or humans. While the eyelids are closed, breathing slows, and snoring may occur, it is entirely different in fish. They don’t have eyelids and their sleep is different.


Fish do not have a comfortable bed or a place to lie down while sleeping. Rather, they go into a resting phase, which is characterized by a lower level of activity . When fish sleep, they no longer react to the environment. They hardly notice noises, light or touch.

It is not clear how deeply fish sleep. However, there is some evidence that the deep sleep phase is comparable to that of mammals. Fish do not close their eyes, but the other behaviors indicate a deep sleep.


Some fish do not come to rest completely even during sleep. With schooling fish it can be observed that they move and adopt a swimming position even in the resting phase . This means that they are still protected in the community and are less noticeable. They cannot be recognized as easy prey by predators.


Some fish species have unique sleeping patterns. The parrotfish, for example, looks for a quiet hiding place and isolates itself with a slime that surrounds its entire body. In this way he prevents his own odor from giving away the position. The natural predators hardly recognize the actually colorful fish and it can relax in its hiding place.

Some fish are characterized by a bright color. This has a particularly attractive effect on the female specimens. When you sleep, the color often changes and changes from a colorful mix to muted tones. An example of this is the doctor fish, which takes on a brownish color when sleeping. As a result, it hardly stands out from its surroundings and appears less conspicuous. This makes him feel more secure and has more peace and quiet so that he can use the night to relax.


For humans, it is true that they are more likely to fall asleep in a dark environment. The sleep hormone melatonin is increasingly released and deep sleep only appears to be possible in a dark room.

It is for this reason that most fish lovers also cover the aquarium. Researchers have confirmed that fish also prefer a dark environment. Melatonin also regulates sleep behavior in them and influences their internal clock. If the aquarium is darkened, less light gets into it and fish fall asleep better.

In bright surroundings , the day-night rhythm is disrupted and sleep disorders can occur. This is often seen in urban environments, which are also brightly lit at night. The cover of the aquarium is useful to the fish to facilitate sleep.


Sleep is also important for fish in order to recover and process what they have experienced. Although research is still divided as to whether fish have sleep phases similar to humans, it has been confirmed that sea creatures enter a deep rest phase.

While they are unable to close their eyelids, they move more slowly and depending on the species, find a cave or other safe place to rest. The fish spends a few hours sleeping and is then fit again to swim lively throughout the day.

So give your fish enough sleep so that it feels comfortable in the aquarium.

Jamie Clark

Hello, I’m Jamie Clark, 32 years old, and I have been living in the USA for a few years.
Since I was a child, I have suffered from a house dust allergy, severely affecting me. I felt the effects both while exercising and while sleeping. Constant sneezing after getting up and difficult breathing were the consequences. The allergy has also developed into asthma, which is still a sporting restriction today.

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