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Do Fish Sleep And How Do They Know When To Sleep?

Fish sleep, but not the same as humans. They enter a sleep-like state and can do so in a variety of ways.  

Do fish sleep is question that requests more explaining than simple yes or no. Fish are resting, because they, like people, need sleep. In this way, they protect their defense system and store energy. This means that their activity in that period decreases significantly, as does their metabolism. 

However, they do not sleep in the same way as terrestrial mammals. Although they are in the sleeping phase, they remain wary of danger all the time. For example, some float in a place while others hide in a safe place such as mud.

There are also fish that are looking for a suitable nest. Not all fish sleep the same. In fact, every fish has a different way of sleeping. For example, some sleep during the day while others use the night to sleep. We must note that fish do not have a REM phase. 

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    How do fish know when they need to go to sleep?

    This is one of the most common dilemmas that people face when they think of fish sleep. So the question is, how do fish know when it’s time to “go to bed”? It is important to distinguish between fish that live in aquariums and those that live in their natural habitat. For example, people who own an aquarium with fish can control their living conditions. This means that after the lights go out at night, the fish become far less active than usual. If you check their activity during the night, you will see how calm they are and that means they are sleeping. However, all fish have an internal clock that tells them when it’s time to sleep, eat, etc.

    an image of a yellow fish preparing for night time

    Unlike dogs that sleep whenever they feel they should to, fish are different. During the night light, they will know that it is time to sleep. Then they will calm down and fall asleep. Keep in mind that there are species that live in very dark places such as caves. There is no sunrise or sunset there, and that makes them quite different from the fish that live on the surface.  

    How do fish sleep?

    Fish may need sleep like all other living things, but the need for sleep is different for each species. Therefore, we can notice a different way of sleeping in fish that differ in anatomy, diet and the requirements of their environment. In that case, we can talk about several different species of fish, and one of the more general divisions is into day and night species.

    For example, freshwater fish swim until they stop at one point, their breathing slows down and they fall asleep. So they are very similar to humans. On the other hand, there are cave fish that have evolved to meet the requirements of their specific environment. As a result, they have poorer vision during the fasting period and reduce the need for sleep. There are also sharks that live in different habitats.

    They move from the salty oceans to freshwater rivers and rest during the day or sleep on the move. They also react very slowly when they are upset during sleep. What is characteristic of most species is that they sleep as if they are half awake and half asleep. When it comes to their place to sleep, they usually go to a corner and sleep there, float in a place or crash into the mud.

    Do fish have sleep cycles as humans do?

    Although fish sleep, it is a slightly different shape from what humans do. This refers to the REM phase as well as closing the eyes, because fish do not have eyelids. So they don’t have same sleep cycles like we do. We can say that most fish have a regular sleep schedule like humans do. However, this is only the case if their sleep is not disturbed or if they are not upset.

    Where do fish like to sleep?

    Since water covers most of the earth’s surface, it is clear that fish have a wide choice of places to sleep. However, they are very creative when it comes to finding a place to sleep. They use different methods, which means that some float in place, others get stuck in the mud, while some find a suitable nest for rest. They are very creative when it comes to finding a place to sleep.

    So some species swim in their sleep. In this way, they ensure the proper flow of water with oxygen into the gills. Some of them in coral reefs even increase the speed of their fins while they are at rest. On the other hand, there are those who float in place. They do not need to move their fins quickly and these are shark-like fish that pump with buccal. They breathe through their mouths and thus push water through their gills. This way they can rest in the water for a really long time. Also, some species of fish that crawl into the sand use the environment as protection.

    an image of a beautiful fish in sea

    It’s their safe way to stay safe during sleep. For example, Lemon sharks do just that by lying on the sandy bottom of the ocean. There are several other ways that fish are used to protect themselves from predators during sleep and this affects their choice of location.

    Can fish suffer from insomnia?

    Fish can also suffer from sleep disorders. This condition is explained by a genetic mutation, which can have different types. Whether it is a common aquarium pet or some other species, it has been proven that there is a possibility of sleep disorders. The most significant data were obtained during the Zebrafish behavior study.

    The mutated gene in them disrupts established sleep patterns, which is very similar to insomnia in humans. The results show that this species slept 30% less than fish without the mutation. The reason is the lack of receptors for hypocretin(orexin). It is a neuropeptide that is responsible for supplying neurons to the part of the brain that controls basic behaviors.

    Due to its characteristics, this species has become a very popular subject of research, and that is precisely because of its nervous system, which is closer to the human one. However, experts say that the solution to the problem of perhaps the network may lie in the evolution that awaits these fish.

    Do fish sleep with eyes open?

    It is easy to spot if some mammal is sleeping, but we cannot say the same for fish. The reason for this is their eyes never close because they don’t have eyelids. They also do not show signs of REM and we know that they are in the sleep phase only because they become inactive.

    an image of puffer fish

    However, the level of inactivity depends on the type of fish. The time of their sleep depends on whether they are nocturnal or diurnal. Because of their appearance, they can see even while sleeping. So they are always ready for any potential risk. Therefore, it would be good to turn off the light in the aquarium, because that way you will provide them with the necessary darkness.

    This will allow your fish to sleep normally. If you are not sure how long they should sleep, turn on the timer to make it easier to establish a day and night routine. They, like all other animals, must sleep regularly in order to stay healthy and live long.

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    Do fish dream?

    It is not yet known whether fish can dream like humans. However, some research conducted on octopuses has shown that they change color. This would lead us to the conclusion that they probably dreamed of hiding predators or stealing their own prey. These would be the reasons why octopuses would change color. We can also compare the sleep of fish with our daily dreams. Although the fish does not actually sleep like a human, it is in a kind of unconsciousness during rest.

    Of course, they do not live in such a safe world as we do, and that is why sleeping is very risky for them. Their brains work in shifts and so different systems rest. Thus, certain bodily functions are excluded for a certain period of time. Therefore, we could compare this condition with daily dreaming. Imagine wandering to your favorite beach during the day while your body is still in your bed at home. In that case, you are not 100% aware of where you are, but you are still careful to catch some noise from the environment.  


    Maybe fish used to be talked about as creatures that are insensitive, do not have the ability to remember, etc. However, later research has just said the opposite. That is why today there are many researches that have proven that fish have something in their heads, and certain species remember or feel pain very well. Some species have contributed to the study of the human nervous system.

    And the reason is a great similarity. All of this tells us that fish are much more complex creatures than we think. Due to their complexity, various issues arise, and one of the most common is related to sleep needs. Fish may not sleep like most animals, but they do have a rest period.

    This is necessary so that they can function properly. It is interesting that different species use this period differently. While some float peacefully, other species make nests or use some other techniques to protect themselves. Also, many of them are able to adapt to different environments.

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