Do Fish Sleep with Their Eyes Open?

*Yawn!* *Stretch!* Do you enjoy sleep? Most children do. Just ask their parents. Of course, it may not appear that way. For instance, when it’s almost bedtime and you want to stay up a little longer to finish watching a movie or playing a video game, sleep may not seem very exciting.

But let’s fast-forward to the next morning! Your alarm goes off, or your mom switches on your light with a cheerful, “Time to get up, sleepyhead!” That’s when you appreciate sleep, right? When the new day calls, we all seem to want a little more sleep.

But what if you couldn’t lie down, close your eyes, and snuggle into your warm, comfortable bed? Would you still desire to spend your time sleeping? Would you even be able to sleep? These are the questions that came to mind when we woke up and fed our pet goldfish.

Do fish sleep? And if they do, HOW do fish sleep? If you’ve ever observed fish for a while, you know they get plenty of exercise. They’re constantly swimming around. It can feel like they never stop. Surely, they need some rest from time to time, don’t they?

As a matter of fact, they do! If you observe fish long enough, you’ll notice that they do take breaks. There are definite periods of time when they seem to hover in place, almost as if they’re in a trance. But their eyes remain open. Are they sleeping?

The simple answer is yes! They are sleeping, and they can sleep at any time during the day or night. Fish sleep with their eyes open because they don’t have eyelids (except for some sharks) to close!

Fish sleep is not exactly like human sleep, though. Firstly, they don’t use pillows. They also don’t have beds with sheets and blankets! For fish, sleep is more like a resting period similar to a daydream that humans might experience.

If you’ve ever owned a goldfish or observed one up close, you’ve probably noticed the times when it’s sleeping. It might hover near the bottom of the tank in a trance-like state. If you put food in the tank during this time, you’ve probably noticed that it takes longer for the goldfish to respond, just like you might have a hard time waking up from a good night’s sleep!

Sometimes people see fish when they’re sleeping and assume they’re awake because they’re still moving. Most fish need to keep moving even when they’re sleeping to maintain a constant flow of water past their gills and ensure a proper oxygen level in their bodies. For larger fish, like sharks, this may involve swimming at a slower rate while sleeping. Smaller fish might only occasionally move their fins.

Certain types of fish are known to sleep in ways that resemble traditional sleep to humans. For example, fish that reside near a coral reef may remain active throughout the day and then hide in crevices in the reef at night to avoid predators.

One particular species of fish does not use a pillow, but it does create a protective covering for itself to sleep in. The parrot fish is able to secrete a jelly-like substance made of mucus, which it surrounds itself with when it’s time to rest. This “sleeping bag” of mucus serves as a shield against predators while the parrot fish is asleep.

Now, let’s try some activities related to today’s Wonder. Before taking a nap, find someone to join you in one or more of the following fun activities:

1. Challenge yourself by planning a family trip to a zoo or aquarium that has a wide variety of fish. Alternatively, you can visit a local pet store that sells fish. Talk to the caretakers and learn about the fish’s life cycles. Find out if they have observed any interesting sleep or resting behaviors in different types of fish. Do different species of fish sleep at different times of the day? Enjoy learning more about fish from an expert!

2. Can you sleep with your eyes open? Most likely not. You probably need a comfortable bed, cozy covers, and a soft pillow to fall asleep. Now, think about your own sleep habits and imagine how they might appear to a fish. You might find it strange how fish sleep, but have you ever wondered what fish would think about your sleep habits? Do you think they would find it strange that you’re not concerned about predators while you sleep? Consider what other aspects of human sleep habits might seem peculiar to fish. Take a fresh look at something you do every night and take for granted, from a fish’s perspective!

3. Explore some previous Wonders of the Day about fish with a friend or family member. You can choose from the following topics:

– How do fish breathe underwater?

– What is a fish tornado?

– Which fish has the largest teeth?

– Do fish swim in schools during the summer?

Enjoy these fishy adventures and discover even more about these fascinating creatures!


1. Do fish sleep with their eyes open?

Yes, fish do sleep with their eyes open. However, it’s important to note that their sleep is quite different from what we experience as humans. Unlike us, fish do not have eyelids to close, so they are unable to shut their eyes while sleeping. Instead, fish enter a state of rest where their brain activity slows down, and they become less responsive to their surroundings. This allows them to conserve energy and recharge for their daily activities.

2. How do fish sleep without eyelids?

Fish have evolved to sleep without eyelids because they live in water. Unlike terrestrial animals, fish do not need to protect their eyes from external elements like dust or debris. Instead, they rely on their environment to provide them with the necessary protection. By keeping their eyes open while sleeping, fish can remain alert to any potential threats or opportunities that may arise. It’s a unique adaptation that has allowed fish to survive and thrive in their aquatic habitats.

3. Can fish sleep in any position?

Yes, fish can sleep in various positions depending on their species and habitat. Some fish prefer to sleep by hovering in the water, while others may rest on the bottom of the ocean or hide in crevices. Some species of fish even have the ability to sleep while swimming by using special adaptations such as locking themselves into position with rocks or coral. The exact sleeping position of a fish is influenced by factors such as their natural behavior, body structure, and the availability of suitable sleeping spots in their environment.

4. How long do fish sleep?

The duration of sleep in fish can vary depending on the species. Generally, fish tend to sleep for shorter periods compared to mammals, averaging around 8 hours a day. However, some species of fish have been observed to sleep for only a few minutes at a time, while others may sleep for longer durations. Factors such as the fish’s size, habitat, and activity levels can influence the amount of sleep they require. It’s important to note that fish do not experience the same deep REM sleep that humans do, as their sleep patterns are adapted to their underwater lifestyle.

5. Do all fish sleep?

Yes, all fish sleep in some form or another. However, the sleeping patterns and behaviors can vary greatly between different species of fish. Some fish may sleep during the day, while others sleep at night. Some species may even exhibit a form of “catnap” sleep, where they briefly rest and then become active again. The ability to sleep is essential for fish to maintain their overall health and well-being. It allows them to conserve energy, repair any damaged tissues, and recharge for their daily activities in their underwater world.

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