Do fish sleep? Answering all underwater slumber related questions

Everyone knows how important sleep is to a person. In fact, without proper rest, many people cannot function normally. It is common to see animals such as dogs or cat sleep, but what about fishes? Do fish sleep? Has anyone seen a pet fish sleep?

This article shall try to cover and answer every question and issue related to the sleep of our aquatic friends. Before getting into the querries, it will be helpful to know why sleep plays such a significant role in every creature’s life.

Why is sleep necessary for all animals?

There are not many studies that explain why animals need to sleep. However, there is enough evidence through research and experiments on why humans need proper sleep. One can assume such reasons to apply to animals like fishes too.

It enhances productivity and increases the ability to concentrate. It helps to regulate energy usage and also revitalizes the body. During sleep, the body of an animal repairs itself to make sure it is ready for another day. Some studies also prove that sleep strengthens the immune system.

Where do fish sleep?

Fishes can sleep where they have been swimming. Some might look for shelters like a leaf or coral before falling asleep. Fishes have natural defense mechanisms to protect themselves while sleeping; thus, most of them do not need a specific spot to rest.

When do fish sleep?

Similar to where fishes sleep, there is no strict timing that they follow when it comes to their sleep routine. Most fishes carry out their daily business during the day and sleep at night, but there are a few nocturnal species.

In some cases, some fish will never sleep even once in their lives. In contrast, some others sleep for a certain period, and never again for a long time.

Do fish sleep like all other living creatures?

Yes, fishes do sleep. After all, they also need adequate rest to keep their body and mind refreshed. Restoring the form and processing of information also occurs when fishes are sleeping. Without sleep, the gills and mouth of aquatic animals start to lag as compared to when they get enough sleep.

When we think of sleep, we expect a pet or other creature to close their eyes and lay on their back or remain motionless. Since no one ever sees fishes behaving this way at any time of the day, it sparks curiosity, and the question “do fish sleep” presents itself.

The reason fishes do not sleep with their eyes closed is that they do not have eyelids like most other animals. These underwater creatures do not rest like humans or pets such as cats and dogs do.

How do fish sleep without closing their eyes or resting on their backs?

If an animal does not have eyelids, it is naturally impossible for them to close their eyes. Thus, fishes can sleep normally and adequately, even without having to shut their eyes.

As for sleeping on their backs, these aquatic creatures do not need beds or floors to rest their bodies. They can do just fine by sleeping in an upright position. Most of the time, these animals are on full alert even while resting to make a quick escape whenever necessary.

On the other hand, fishes like sharks need to keep moving or swimming so that water passes through their gills. If they do not keep moving, their gills will not be able to extract enough oxygen to keep the body functioning.

How to know when a fish is sleeping

The sleeping behavior of fishes is not as apparent as other animals, and thus, it might be slightly challenging to spot a sleeping fish. One sure giveaway that anyone can notice to figure out that a fish is sleeping is when it is less active than other hours of the day.

It will still have its eyes open and might make some small movements, but they will be much less energetic. These subtle movements allow the creature to maintain balance. Most fishes slowly sink towards the bottom, although they will not lay down fully. Some species may even stop moving altogether.


In short, fishes do sleep just like any other animal to function correctly during their active hours. They can sleep with their eyes open in an upright or swimming position. In case a fish is “sleeping” on its back, this peculiar behavior might mean that it is not feeling very well.

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