Do fish in aquarium sleep?

Table of Contents

Fishes differ from land mammals, but that does not mean they do not have similar characteristics; they eat, sleep, play, and even get sick. When animals get tired and weak, they rest, or they go to sleep to enable them to carry out their day-to-day functions well and with vigour. This phenomenon is the same in fishes, well, almost the same because fishes might not outright close their eyes to sleep. That does not mean that they do not sleep; it only means the method of sleeping is different in fishes as when compared to other mammals or even birds. 

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Fishes do not possess eyelids like other animals, so when they sleep, their eyes might be open because of this absence of eyelids. Although they do not have eyelids, there is a significant decrease in activities in fishes when they are about to rest. There are different places a fish in an aquarium might want to sleep, either floating or even at rock bottom. There is a decrease in the metabolic functions of the fish when it’s asleep. Although, we might not be able to see the metabolic functions in the fish to know if they are reduced or not. The way we are able to observe a sleeping fish is when we notice inactivity in the fish. A sleeping fish might even stay afloat as though it’s dead, but to know if it’s dead or not, you can carry it. If it’s carried, you will notice it wiggling, trying to get away. This is because even though they are asleep, fish are watchful of upcoming dangers. So, yes, aquarium fishes sleep, just like other animals.

Do fish in aquarium sleep
Do fish in aquarium sleep

How Can You Tell A Fish Is Asleep?

It’s relatively easier to tell when other animals are asleep. Just like in dogs and other household pets that are mammals, you would see the eyelids close to be able to tell that they are sleeping or in a restful state. It is quite different in fishes because of their lack of eyelids, and they do not have the part of the brain called the neocortex, which is responsible for sleep. However, there are other ways we can know when a fish is sleeping. Sometimes, fishes might sleep at the bottom of the tank, and when they are sleeping down there, there is a complete reduction of activities or a complete stop in activities. With this, you can know when a fish is sleeping or not. Some even stay afloat without being even the least bit physically active. 

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The definition of sleep in fishes is quite different from ours. It is basically slowed metabolism or no physical activity to conserve energy in their body. The definition of sleep in fishes is equivalent to the definition of rest in humans and other mammals. Sometimes, when you look at a fish, swimming slowly around the aquarium or fish tank, not lazy swimming but laboured swimming; extremely slow, it is a sign that the fish is sleeping. A fish might cling to a coral in an aquarium and stay steady and unmoving; this is a sign that the fish is actually sleeping. A fish might also hide under a rock and remain physically inactive or even static like it is dead; this is a sign that it might actually be sleeping. If you are a fish enthusiast, it might be quite easy to tell between when a fish is sick or when it is just sleeping. Also, if they are unresponsive to what goes on around them, it is possible that they are asleep.

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How Long Does A Fish Sleep?

In humans, we only have the recommended duration that a healthy person can sleep; it cannot be said that all humans sleep for a particular amount of hours. If it is said, it would be wrong because some people actually sleep for 2 hours, some for four, five, six, and eight, as the case may be. This is the same in fishes, and fishes do not have a particular amount of time they sleep and wake up. Some fishes are nocturnal, and just as the name goes, they are particularly inactive during the day and active during the night. This inactivity they experience during the day is just them sleeping and resting. In other words, the sleeping duration in fishes varies from fish to fish. 

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There are some factors to consider when talking about the duration fish sleep. Factors like; size, species, and types should be considered when talking about the duration of time fish sleep. The range of the duration of fish sleep is within the range of 8-12hours. The fishes that are bigger and lazier than the other fishes tend to sleep more than the other fishes. The smaller and smarter fishes usually have a shorter sleep cycle than other fishes because of their want for exploration and their young age. The nocturnal and day fishes are classified under the types of fishes when trying to discover the time in which some fishes sleep and the physiology of their sleep. Although some fishes in the wild don’t sleep at all, they swim continuously, probably because of predators. As said earlier, fishes know when there is danger around, and in such situations, they don’t sleep.

Do Fish Swim When They Are Sleeping?

Fishes are different in behaviour; some fishes might stay at the bottom of the aquarium, reef, or wherever they want to station. Some fishes might be stationed at their spot, motionless and conserving lots of energy. It’s easier for fishes that stay afloat at the surface of the water to do this because they can get sufficient oxygen from the water and atmospheric oxygen, also. Notwithstanding, not all fishes can do this; that is, stay motionless till they awaken. Most fishes, adult fishes, try to stay swimming while they are sleeping. As they swim with open eyes and slowly, it’s as though they are in a trance or daydreaming and not actually sleeping. The main reason most of them swim while they sleep is to maintain the oxygen transfer from the water body and their body. 

Fishes, just like us, need an adequate amount of oxygen to survive without dying off. Hence, why they swim while being in a restful state. The swimming fishes do when they are sleeping is not fast; it’s really slow because they are resting and the rate of their metabolic activities is reduced. When the swimming is fast, it shows that the fish is awake and no longer asleep. In the case of some smaller fishes, they might not necessarily swim to maintain oxygen exchange in their body. They might do as little as flapping their fins to direct the water towards their gills to facilitate oxygen exchange with the surrounding water body. No matter the type or size of fish, there needs to be at least a little kind of movement to propel the water to the gills of the fish.

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Do Aquarium Fish Need Darkness?

In nature, we have night times to help us know when it’s late, and we need to sleep in order to replenish our energy. Even in the wild, the daylight cycle makes it possible for animals to regulate their activities and know when to sleep and when to wake up. During the day, all the animals may be active, especially if they are not nocturnal; these active animals also retire to bed when it’s late, looking for a place to make their sleeping comfortable. It’s almost the same in fishes because the fishes, just like other animals, also recognise the light and day cycle. Despite the fact that they lack the neocortex of the brain, they are likely to become inactive if the aquarium lights are put off. More like a nighttime routine for them. 

Excess lights in the aquarium are actually not healthy for the fishes; it can cause competition, which can lead to fighting, and fighting is very bad for fishes because it stresses them. It’s actually important to provide the aquarium with darkness because of this reason to avoid fish killing. Also, turning off the aquarium lights at night actually helps to make the fishes be comfortable as though they are in their natural habitat. However, excess darkness in an aquarium containing fishes can make them lose their colouration and become pale and abnormally coloured. Also, alternating between light and darkness helps the fish tank not to be dirty. The dirtiness is caused by the increased growth of algae, which is caused by constant light. These algae can even cause reduced oxygen concentration in the water, which can cause a fish to kill. However, excess darkness is not advisable; alternating between light and dark times is very important.

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Do Fish Sleep At The Bottom Of The Tank?

Some fishes are top feeders, while others feed on the bottom of the tank. Most bottom feeder fishes not only eat the bottom of the tank, but they also sleep there. However, sometimes fishes stay at the bottom of the tank because they are stressed because they are bullied by another fish, or the living conditions in the tank are not good. Not all staying at the bottom motionless, or making little movements, is a case of sleep. That’s why it’s very important to watch our fishes, in order to know if there is something wrong with them. When they stay at the bottom, it’s not always to sleep. It’s sometimes because they are ill and are about to die. Illnesses make fishes go down to the bottom and stay inactive throughout the period of their stay there. Sometimes there are other signs that show that a fish is sick and not just resting. These signs are; spots on the fins, discoloration in the fish, and periodic hitting or scratching themselves against the tank, aquarium, or fishbowl.

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Do Fish Sleep On Their Side

Humans, and some other mammals, have the ability to sleep on their side in a more comfortable place. This is a sign of higher intelligence, which cannot be overlooked. In mammals, when they want to sleep, they close their eyes and most times find a suitable way to sleep, even if it’s on their side, on their back, or even faced down. These ways of sleeping are used in order to achieve a particular type of comfort. However, this kind of luxury is not affordable to the fishes. They do not have a developed brain; in their brain, there is no neocortex that can help control sleep. Hence, they do not have the ability to close their eyes or even know a comfortable way to sleep. However, some species produce mucus to encompass them when they are about to sleep, almost similar to a transparent sleeping bag. Furthermore, there is an exception to fishes not sleeping on their side. The betta fish has a form of intelligence quite similar to humans or mammals. They would even go as far as finding a place to sleep and then sleeping on their side in order to be comfortable. There are also few other fishes that do this. However, it’s not a norm for fishes to sleep on their side.

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Fish Sleeping At The Top Of The Tank

Not all fishes go to the bottom of the tank when they are about to sleep. Just as we have bottom-feeding fishes, we also have top feeders. Top feeders usually swim close to the surface of the water to do everything, including sleeping. That is why it’s important to know the type of fish your fish is, so it would not be a thing of surprise when you see it floating near the surface of the tank and inactive.

Do Fish Sleep Upside Down?

Most times, fishes swim upright when playing or even just casually swimming. This upright position they try to maintain is also the same position they maintain when they are asleep. If a fish is relatively inactive and making small movements upside down, the fish is not sleeping; it’s sick and should be taken care of medically. When this is seen, it’s also important to monitor the living conditions of the fish if it’s favourable enough.

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Do Goldfish Sleep?

In animals, sleeping can be known as closing the eyes and being in a completely restful state. However, this is not the same when we are considering goldfishes. Goldfishes, just like other fishes, do not have eyelids that they can close. So, when a goldfish is sleeping, you might see its eyes open because of its inability to close them. The open eyes are only one of the many other differences the goldfish has when compared to other animals. When most mammals sleep, there isn’t just a closing of eyes. There is also a norm of staying static or at a particular position when sleeping. This aforementioned behaviour is something that cannot be done by goldfish because they need oxygen to be able to stay alive in the water. Goldfishes, just like other fishes, respire by propelling the water into their gills by movement. This is why a goldfish might keep swimming even though it’s fast asleep. Although the movement is reduced and slow, it’s still noticeable and easy to tell that the goldfish is resting or sleeping. There is a colour fade phenomenon that happens when the goldfish is asleep to ward off predators away from them, similar to a dog playing dead. 

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How Long Do Betta Fish Sleep?

There is no specific amount of time a betta fish should sleep in an aquarium. In humans, the light and dark cycle helps us regulate the way we sleep and when we sleep. This is not different in betta fishes; they follow this sleep pattern, especially when the light in the aquarium is turned off. Betta fishes also anchor on surfaces like leaves or even logs to sleep when the aquarium light is turned off. This is why it’s very important to mimic the day and night cycle when you have an aquarium to enable the bettas, have an adequate amount of sleep. When they do not have adequate time for sleeping, it can lead to some problems, and it can also be due to inadequate care from their owner to them. Nonetheless, there is a range of duration that is recommended for a betta fish to sleep; this duration excludes the usually short afternoon nap they take to help rejuvenate them. Although the recommended duration is and cannot be applied to fishes, it’s still healthy to give bettas a longer time in the dark than in the light. Twelve to sixteen hours is recommended to be given to the betta so that it can enjoy an ample time of inactivity, even though it might not sleep up to even twelve hours.

 

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Conclusion

As we have seen so far, fishes that are kept in an aquarium do sleep, just like those existing in the wilds. However, when a fish sleeps, it is not usually like that of other animals but more like a hibernating process.

Hazel Buckley
Hazel Buckley

About Hazel Buckley
Hazel is an animal enthusiast and educator who grew up on a farm which her parents owned in Ingogo, KwaZulu-Natal, South Africa.  The farm was situated right under the Majuba Mountains - the site where the Anglo-Boer War was fought. 

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