How do Fish Sleep

Last Updated on September 18, 2021 by cmoarz

To rejuvenate their bodies, process information from the day, and “recharge their batteries,” most animals need to sleep – or rest – at set intervals.

The most obvious sign that animals are sleeping is that they shut their eyes, recline back, and ignore gentle touch.

It’s really easy to tell when fluffy the cat is sleeping Because it’s so very normal and obvious to us. But what about fish, How do fish sleep?

When humans sleep, a portion of the brain – the neocortex – shuts down. The issue with fish is that they (most anyway, there are some exceptions) don’t have eyelids to keep their eyes closed, and they don’t have a neocortex. 

It also raises the question, “Do fish sleep?” And, if they do, how do they accomplish it, where do they do it, and when and how often, and how can we tell when they are resting?

Although fish do not sleep in the same manner that humans do, most species appear to enter a restful state with reduced breathing and metabolic rates, as well as decreased brain activity, according to researchers.

This encourages a healthy and disease-resistant lifestyle. So, essentially, fish do “sleep,” but it’s in a form that we’re unfamiliar with other animals.

So, How Do Fish Sleep?

When fish sleep, they frequently remain motionless, their breathing slows down, and some can even be grasped in the hand as most aquarium hobbyists will attest to.

Zebra Danios, like humans, sleep in a similar manner, according to researchers at Stanford University. They were also able to identify slow-wave sleep as well as paradoxical sleep (deep sleeping) in the fish, just like mammals, birds, and reptiles.

The only distinction was that, unlike humans and other animals, they did not exhibit Rapid Eye Movement (REM) during paradoxical sleep. We assume its because they don’t need, and can’t, close their eyes.

When a shark is resting, it must move to ventilate its gills, even if other fish remain motionless. If it doesn’t, it could suffocate.

A very interesting discovery, some species of marine Parrotfish and Wrasses build a mucus cocoon around themselves when they sleep. Parasites and predators may be deterred by this slime sheet, according to scientists.

Where Do Fish Sleep?

Depending on the species, fish may rest in a number of ways. Some recline on the bottom or even burrow themselves in the sand, while others hide in grottos or caves, some hover or drift near the surface and occasionally flick a fin to stay balanced, and some nestle into plants, driftwood, corals, or other things and just sort of hang there from time to time.

Any aquarium owner would be terrified to discover their fish laying on the bottom or “stuck” in an ornament or hollow log, but many aquarium species do this while resting.

But as any aquarist can attest to, When you see your fish laying around motionless, It’s scary because you think it could be dead!

When Do Fish Sleep?

Fish, according to experts, have similar sleep habits to humans and other animals.

The majority of aquarium fish are diurnal, which means they move about during the day and sleep at night. This is likely a learned behavior.

Some species, on the other hand, are nocturnal and prey during the night, resting during the day in places you usually can’t see and enjoy them.

Some catfish and plecos, as well as some knife fish, loaches, and other species, are included in this group.

This can sometimes pose an issue depending on the fish you have shared in an aquarium. Sometimes night sleepers end up being easy prey for larger night stalkers.

Fish that are caring for the young don’t generally sleep, and researchers have also discovered that some fish, such as Tilapia, do not begin to sleep until they are 5 to 6 months old.

How Do I Determine If My Fish Are Sleeping?

Here are some signs that your fish are sleeping:

  • They lie still for periods of time.
  • They rest on the bottom or upon something in the aquarium.
  • They are totally unaffected by what is going on around them.
  • This is known as the “summer constipate,” and they generally do it in the evening, when the aquarium light is switched off.
  • When you see it, your first instinct is “Oh crap my fish died”

 Do Fish Have Sleep Disorders Like Humans and Other Mammals?

Fish sleep hasn’t been studied extensively by scientists, but it was discovered in studies on Zebra Danios that when they were deprived of sleep for a few days with a mild electrical current, they slept more when returned to a regular day/night cycle rather than being disturbed. When Zebra Danios were confined to a dark cage for several days, however, they slept normally once returned to a normal day/night cycle. Researchers believe that light may block the sleep-inducing hormone melatonin in Zebra Danios, but there is still a lot of work to be done in this area.

Are My Fish Sleeping Enough?

The simplest approach to ensure that your fish are resting adequately is to use a timer on your aquarium light, providing them with a standard day and night routine.

Make sure your aquarium has plenty of protection for all of your fish, so they can feel safe and secure when they rest. If your fish are in a room where the overhead light is on, you should move them to a darker room or somewhere where there is additional light pollution.

Fish, like all other animals, need to rest on a regular basis in order to stay healthy and live longer.

Specific Fish Sleeping Patterns

How do guppies sleep

Guppies cease swimming and float to sleep, seeming dead in some cases.

Guppies may rest on the gravel at the bottom of a tank, float near to the surface, or recline beside plant decorations.

They are in a silent state of relaxation when they have no observable eye movements and a decreased respiratory activity rate.

They do not experience REM sleep, and their brain waves do not change. The fish’s hearing and tactile senses also become less acute. When the lights are turned off, guppies that have been kept in a freshwater tank typically cease to move after a period of time.

If you wake up early enough, You can watch them slowly start to wake up.

How Do Whales Sleep?

Conscious Breathing So They Don’t Drown

The cetaceans’ ability to remain awake and keep their blowhole at the surface of the water in order to breathe has earned them the name “conscious breathers.”

Because of their inactivity, this self-regulatory approach requires them to keep at least a portion of their brain awake in order to breathe. Human respiratory systems are different since they are involuntary.

We can breathe even when our conscious mind is asleep, thanks to our involuntary respiratory system. If a Killer Whale fell asleep in the same manner that we do, they would be in danger of drowning.

Some Will Sleep With One Eye Open

Some whales and dolphins modify their sleeping habits in order to only allow one hemisphere of their brain to sleep at a time. The remaining half of its brain, as well as the opposite eye, is kept active by the whale. When it reaches the surface,

Whales rely on their half-brain’s attentiveness to keep track of pod members, as well as watch for predators and barriers, which is why they’re able to do it. After a period of two hours, the whale reverses this procedure by rested the active brain side and woke up the sleeping half. This process is sometimes known as “cat-napping.”

Other larger Cetaceans, such as Sperm Whales, are able to maintain complete buoyancy while sleeping and stay still underwater. These creatures have a bigger breathing apparatus than Orca, allowing them to exchange more air with each breath and tolerate CO2 better.

Whales can actually sleep with one eye open. (in addition to one brain hemisphere being awake) To recall to breathe, they may do so. They can also hold their breaths for lengthy periods of time, in which case they may fall asleep between breaths.

How Do Corydoras Sleep?

This is one of those “oh crap my fish is dead” situations that often happens to new cory owners.

This is because the corydoras have a tendency to sleep either on its back or its side, laying motionless on the substrate.

Many new cory owners freak out and assume their fish has died, when in fact all they’re looking at is a sleeping corydora.

You can usually differentiate between a healthy (or “live”) corydora and one that’s dead by observing its breathing pattern/behavior.

However, if you are worried, go ahead and gently poke it with a stick! Or just turn the lights on :).

How Do Betta Fish Sleep?

Betta fish, like humans, sleep at night. When resting, they become motionless and their eyes are opened because of the lack of eyelids. While sleeping, betta fish may change color (it’s a natural form of self-defense), and they can sleep in a variety of postures: curled up like a cat, on one side, or even vertically, with the head down. Some bettas can also fall asleep with their fins spread out.

A beta fish will sleep for about 12-14 hours a day, but as such light sleepers, it’s hard to catch their moments of rest.

Betta fish don’t typically show the motionless, “sleeping on their side” behavior that other less-active pets do.

They will sleep normally at night time and during naps, but they can stay somewhat active throughout resting periods without damage to the health or well-being of your betta.

And it’s a good thing too, as there is much for us to learn about our beloved pets from watching them sleep – who knows what mysteries we might solve! 🙂


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!