Skip to main content

Do fish sleep? It’s complicated

You'll probably find your fish resting periodically — don't panic

Fish resting in an aquarium
Fahad AlAni / Pexels

You might see your little swimmers still and peaceful in your tank and think that they’re sleeping. But do fish sleep? It’s complicated because first we have to define what sleep even means. Research says that many animals do rest and that slowing down intermittently helps with all sorts of processes, including things like fighting disease and recharging energy. So while fish don’t sleep in the same way humans and most other mammals do, they still rest periodically to help them stay sharp.

How do fish sleep?

First, let’s talk about our sleep. You’ll notice that when we go down for the night, we almost always close our eyes and our furry friends do as well. That’s thanks to our neocortex, which shuts off so we can get some shut-eye every night. Dogs and cats operate much the same, though they sleep at different times than we do (practically all day, in the case of cats).

Recommended Videos

Fish have neither a neocortex nor eyelids, meaning they can’t sleep exactly the same way as humans. Researchers at Stanford studied fish brains and found that they do seem to be sleeping, though aquatic animals likely don’t enter REM state (dolphins, too, have slightly different sleep methods). Sharks take this even further by swimming even during sleep — if they stop, they won’t be able to keep breathing!

When do fish sleep?

You may be surprised to discover that fish usually sleep at night and spend the day awake. That’s great for us to get prime-time aquarium viewing. Still, some fish are up at night, especially a few species of catfish that will do the bulk of their feeding in the wee hours of the morning. Interestingly, a few fish don’t sleep at all, including some species of cavefish that live entirely in darkness, and many baby fish, which don’t develop this ability until adulthood.

How do I know if my fish are sleeping?

As with all animals, you probably want to leave your tiny sea creatures alone while they get some rest. You don’t want to get woken up from a nap, either, after all. Check for signs that they’re catching a few z’s. Fish are possibly sleeping when they stay motionless for a while, lay down on something in the tank, and don’t respond to things going around them. So if you walk up to your fish house and see one snuggled up in the corner, they’re probably fine. Come back later to make sure they’ve moved rather than tapping on their home to rouse them.

While fish might not sleep as humans do, they still rest, usually daily and at night. Don’t be surprised if you see your tank inhabitants snoozing off and on throughout the day and much of the night. Also, set up your area to make sure the fish have a quiet, dark place to retreat to and that the ambiance in the evening gives off a sleepy vibe.

Rebekkah Adams
Rebekkah’s been a writer and editor for more than 10 years, both in print and digital. In addition to writing about pets…
How long do guinea pigs live? Here’s what to know
Follow these tips to keep your pet guinea pig around a long time
Guinea pig on hay

When choosing the right pet for you, the first question you might ask is how many years of enjoyment you can expect from them. It is a great question, but the answer can vary depending on the animal. So how long do guinea pigs live? Read on for the answer — and how to help increase your little pig's lifespan.

How long do guinea pigs live?
It is important to note that a guinea pig is not a hamster. A lot of pet owners do not know the difference and think these animals have similar life expectancies. However, they are actually quite different! There are several breeds of hamsters and this can affect how long they live, but a normal hamster can live for two to three years depending on how they are treated.

Read more
How to tell if your snake is sleeping
Useful tips to determine if your snake is getting their z's
Green snake curled up over a branch

Just like all living beings, snakes need to catch some z's to rest and restore themselves. According to new research, believe it or not, reptiles experience REM sleep and they even dream, just like humans. But how to tell if your snake is sleeping? It can be quite the challenge, since you won't be able to rely on seeing your snake's closed eyes as a sign. Instead, you'll learn to look for other signs that could indicate your pet is napping.

Taking the time to learn these signs will allow you to properly care for your pet snake and will keep you both much safer, especially if you need to handle them and don't want to inadvertently interrupt their snooze fest. Let's take a look at some of the indicators that will let you know that your slithery friend is, indeed, fast asleep.

Read more
Why do hamsters sleep so much? When to be concerned about their health
This is why your hamster sleeps all day
Hamster sleeps in a small wooden house in his cage

You may be jealous to learn that hamsters sleep up to 14 hours per day (wouldn't that be nice?). But unlike humans, they don't do it all in one fell swoop, instead waking and napping at many intervals throughout the day (and sometimes night). They're also nocturnal, so you will likely see (or hear) them playing and running on the hamster wheel very late.

Luckily, with the right routine, you can still spend good quality time with your pet by timing it to fit both of your schedules. If you're wondering why your hamster sleeps so much even for a rodent, it may be time to visit to the vet and see if there's more to it.

Read more