Do Fish Sleep? How Long Do Fish Sleep For? (Answered)

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why don't fish sleep

Almost all the living beings on earth sleep. It is crucial for revitalizing the soul and body. But, when we say that all living beings sleep, a few don’t sleep, like jellyfish, bullfrogs, insects, baby dolphins, etc. And they survive okay without sleep. But, today’s question is about do fish sleep?

Then there comes the fish, even though it is a common misconception that fish don’t sleep and that they are always swimming here and there, feeding.

But, the truth is that almost all fish do sleep. The only reason that they look like they are not sleeping is because they don’t have eyelids, and their eyes are always open.

Some fish sleep during the daytime, while some sleep during the night, just like the animals and other living beings. It is easy to tell what fish look like when they sleep asleep because they become motionless when sleeping.

There are several other things that you should know about how do fish sleep.


Understanding Fish Sleep: The Stages of Fish Sleep


As fish don’t have eyelids, they don’t look very different when asleep or up. Therefore, it is sometimes impossible to determine whether the fish is awake or sleeping. But, if a fish is a little less responsive or not responsive at all, then probably it is sleeping.

Although, most fish are diurnal. The rate of fish death is highest during the first few hours after sunset because fishes are more prone to getting attacked by predators when they are less alert while sleeping.

image of a three colored pet fish

But, did you know that not only do fish sleep, but they also have elaborate stages of sleep, which are obviously different from any living being’s cycle.

Humans go through four stages of sleep (2 stages of light sleep, one stage of slow-wave sleep or deep sleep, and the final stage of rapid eye movement or REM) and have a neocortex.

Fish, however, do not have a neocortex, but they still go through two stages of sleep that are human equivalent to the slow-wave sleep or deep sleep stage and rapid eye movement or REM sleep.

If fish don’t get enough sleep, they become vulnerable to adverse effects of it. Most fish experience sleep rebound, which means they try to catch up on lost sleep.

Like humans, fish must get the minimum acceptable sleep their body requires. If their sleep is interrupted at their desired time, they pass into a microsleep in which they try to get half of their normal sleep needed.

A disturbed sleep cycle in fish can lead to stress and getting sick. In nature, fish finds a way to full their required hours of sleep. But, if you have a pet fish and you don’t let it sleep as much as it should, then your pet can seriously get sick or even die of stress.


Estivation Vs Sleep


Estivation is the state where animals adopt a corporal torpor for surviving for longer durations, just like hibernation in polar bears and snakes.

They adopt this condition because of high temperatures and sterile conditions without water and food. Estivation is the inactivity of the body with a lower metabolism. Usually, animals estivate in hot and dry seasons (usually in the summer months).

Fishes create a kind of cocoon around themselves of dried mucus or shed epidermal layers when they estivate. The cocoon helps protect them from water loss. It covers their body entirely except their nostrils.

Fish don’t sleep like the rest of the mammals. Because their sleep pattern varies from fish to fish, some fish float, some find a safe spot in the coral or caves, and others build mud nests to sleep. This rest period for fish is similar to the sleep humans get for restoring their bodies.

Usually, estivation helps fish to survive a season or year with the scarcity of food or dryness. But, when they have enough food to forge, they sleep for the rest of the time.


Do Fish Suffer From Sleep Disorders? 


Fish sleep disorder or fish insomnia are real things that we learned about when scientists studied the sleep patterns of fish. It was discovered that aquarium fish and other fish in general, like zebrafish, could develop mutations that are due to sleep insomnia.

But, what doesn’t happen is that if a fish has stayed awake at night because of any reason, then it will not sleep in the day to compensate for the lost sleep.

Usually, researches have been conducted on zebrafish because they are easier and cheaper to breed than mice, and they also have a backbone that is closely similar to humans. 

Many fish suffer from sleep insomnia similar to humans if they are kept too long from sleep.


Where Do Fish Sleep?


Different fish species have different sleeping habits and places where they like to sleep.

For example, some fish like to lay on the bottom of the surface of the sea or ocean and bury themselves in the sand, while others want to hide in any kind of openings, grottos, or caves that they think will keep them safe from predators.

Then there are fish who like to hover motionlessly near the surface or the bottom of the water, and some fish like to settle in corals, plants, driftwood, or any other object.

image of striped fish

Fish like sharks and tuna keep swimming while sleeping because they have to breathe while swimming. Parrotfish create a mucus cocoon around themselves every night so that no predator or parasite might attack them.

Whales put parts of their brain to sleep so that they stay conscious and asleep at the same time while swimming.

Usually, when a fish is motionless anywhere in the waters, it means that they are asleep and can be asleep anywhere they feel comfortable.


When Do Fish Sleep? 


Like other mammals and humans, every fish also has a sleeping routine. Mostly the fish are either diurnal or nocturnal. Diurnal means that they stay active at day and rest at night.

Nocturnal meaning that they roam around at night for food and sleep at daytime in caves and crevices. Aquarium fish are primarily diurnal.

Fish like catfish, loaches, and knife fish are nocturnal creatures, while neons, diurnal fish, are sleeping peacefully at night at the bottom of the waters, the catfish are roaming around looking for food.

Most of the time, when new fry hatch, their parents don’t sleep because they have to care for them at least for a few days. Then there are some fish like tilapia who doesn’t sleep until they are 5-6 months old.

Fish also don’t sleep when they migrate. And finally, the blind cavefish don’t sleep because they are blind and always in the dark.

Just like a human’s internal clock tells them when it is time to sleep. Similarly, fish have an internal clock that tells them when to sleep.


How Do I Make Sure My Fish Get Enough Sleep?


It is necessary for all fish to rest in one way or another. Good quality sleep is required for fish to follow their physiological cycle. But, since aquarium fish can’t differentiate between day and night naturally, you have to help them identify.

The easiest way to ensure that your fish is sleeping as much as it should is to put a light timer on your aquarium’s light. This way, your fish will get into the habit of the proper routine of day and night.

Another way to ensure that your fish gets enough sleep is to provide enough shade to it so that they feel safe and sleep peacefully.

Like every animal on the planet, fish also require sleep to live healthy and happy. So, if you really want to keep your fish happy in your house, you must give them the best conditions to sleep along with other things like food, care, love, and cleanliness.


Is Your Fish Asleep?


Sleeping fish is very much different from active and awake fish. An awake fish will move around its aquarium all the time, only stopping for short intervals. If you give it food, it will dash towards the surface to eat it, and if you touch or tap the aquarium’s glass, it will respond.

image of a fish with human like lips

On the other hand, a sleeping fish won’t do any such thing. It will lay motionless on the bottom of the aquarium or in a cave.

They won’t dash to eat the food if you sprinkle some while they are asleep, and they won’t respond to a slight nudge or tap on the glass (unless that tap is thunderous and makes them fear for their life, then they will respond).

They are not very conscious of the activities going on around them. If you silently and carefully observe your inactive fish, then you will see that they are breathing very slowly. Here are a few pointers to notice the next time your fish is inactive to ensure that your fish is asleep:

  • They don’t move for a few minutes.
  • They are floating in one place or have withdrawn to the surface or the bottom of the aquarium.
  • They take longer to respond to things like food and taps.
  • They are inactive at the same time every day.

The Conclusion:

Now that you have read about your sleeping fish, you can take care of them in a better way. Fish sleep (except for a few species), and there is no reason to believe otherwise. The only difference is that every species varies in their sleep.

I have tried my best to answer everything about fish and their sleep. From the aquarium to wild deep waters, I’ve covered it all; so that you may understand more about your fish and other fish in general.

But, there must still be some questions that are in your mind regarding why don’t fish sleep, how long do fish sleep for, what do fish do when they sleep and fish’s sleep schedule. So, let’s take a look at some frequently asked questions:


Frequently Asked Questions

#1 – How Do I Know If My Fish Are Sleeping?

It is very easy to tell when your fish is asleep. They become motionless and float to the bottom or surface of the water.

They also become less responsive to things around them, like taping the glass and sprinkling food. But when you notice them carefully, you will notice that they are breathing very slowly.

#2 – What do aquarium fish sleep or do at night?

Most aquarium fish are diurnal, which means that they sleep and rest at night and roam around in the daytime. However, you might also have a few nocturnal fish in your aquarium, which means they will creep at night and spend days resting and sleeping. 

#3 – Do fish need lights off at night?

Aquarium fish don’t need light the whole time. I suggest that you turn off your aquarium light during the night so that they rest properly.

If you keep the light on the entire time, the fish can get stressed and sick eventually. Too much light can also cause algae to grow in the aquarium quicker than usual. So, don’t keep the light on at night.

#4 – What Else Can Impact Fish Sleep Patterns?

Many things affect the sleep patterns of the fish. Few are the temperature of water and availability of food. 

#5 – Do All Fish Sleep In The Same Way?

No, all fish don’t sleep the same way. Some reduce their activity and slow down their metabolism, while some sleep in various parts (one part of the brain at one time)—the way how fish sleep is different from that of other animals and humans.

However, most aquarium fish sleep in the same way by floating at the bottom of the aquarium or inside the caves.

#6 – Do Fish Sleep with Their Eyes Open?

Yes! Fish sleep with their eyes open because they don’t have eyelids to shut them. Only a few fish species like sharks have eyelids.

The whole confusion about whether or not the fish sleep is because they sleep with their eyes open, and it is tough to identify when they are sleeping or awake.

The only way to tell if a fish is asleep is to notice when it is inactive and has slow breathing. If you are wondering do goldfish sleep with their eyes open, then the answer is yes! They do.

#7 – Can fish sleep upside-down?

Fish can sleep upside-down but mostly, the fish stay stationary and in the same position when sleeping. They don’t turn sideways or upside-down. All they do is float to the bottom and sleep there but in an upright position. 

#8 – Do fish swim when they sleep?

Most fish do swim while they are sleeping. They keep floating, maybe unconsciously, because they have to keep a constant water flow.

Some fish like whales keep one part of their brains active at all times so that they may float and keep swimming flawlessly. Fish swim slowly when asleep, but they do swim and float.

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