Who doesn’t love it? Perhaps the only thing that we as a human cohesion can agree upon is the fact that everyone enjoys sleep. Be it a nap when you’re supposed to be working, or a warm cuddle with your imaginary lover; sleeping has always made humans realize that at the end of the day, all we need is a little reset button and we’re good to go.

The human sleep pattern is definitely a subject of interest. But did you know that animal sleeping patterns are far more intriguing? Take the albatross for example. It can sleep while flying, and be consciously aware of its surroundings and potential predators. Then there are animals that don’t sleep that much, such as the bullfrog and the dolphin. Then there are animals that sleep too often, as much as 20 hours a day, like the lion and most big cats (some humans can be found in the same condition too).

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With that being said, perhaps nothing intrigues us and our children more than the sleep patterns of a fish. Yes, that’s right. Even those tiny little creatures that go glub-glub are more interesting than your usual Netflix and chill routine. So the question from our childhood still remains: do fish sleep?

Let’s take a dive into it! (No pun intended)

What Is Sleep?

What Is Sleep

Ah, yes. Sleep. What the heck is it? Although the common public may define it as “the best thing in the world, that’s what”, scientists would like to differ. First and foremost, it is defined as a natural bodily function by which a living organism loses consciousness and has inhibited reaction to stimuli. Basically, a sleeping creature most likely will not feel anything, and will most likely not act voluntarily, though involuntary functions like breathing and blood pressure will persist.

Though the process of nap is widely understood, the cause remains a mystery. From immune system recovery to extraterrestrial interventions, the theories just get wilder and wilder. And we may never know the true function of a nap. But hey, at least it’s fun.

Sleep In Fish

When it comes to fish, however, sleep can be defined as a bit more uninteresting. Sleeping, or “resting” as the experts prefer to call it, is the state of trance-like daydreaming where a fish’s behavioral pattern is similar to that found in most sleeping mammals. The only difference? Fish have neither eyelids nor a neocortex, and hence you can never know when they’re asleep.

Most fish are even capable of swimming during their snooze time since they need to constantly keep moving to keep the water rushing through their gills. Some fish may even seek shelter in corals and anemones or caves right before their nightly routine. But the concept of nocturnal unconsciousness is, for the most part, still a mystery when it comes to these chubby water dwellers.

Behavioral Aspects

The behavior of mammals during nap time is quite simple: they shut their eyes, remain unconscious, and sometimes might even talk about their favorite TV shows. But for the fish, we’d like to differ. Fish (excluding sharks) have no eyelids and only remain semi-conscious. Most fish are even known to swim during their sleep. It can be defined as a state of prolonged inactivity and little to no response to stimuli. That criterion holds true for most marine animals. The brown bullhead, for example, is known to “sleep” with its fins and tail outstretched and body inclined to a certain angle, while also showing little to no response to touch.

Shelters, or “Beds”

Shelters, or “Beds”

While most of us are used to napping in our comfy little beds, it seems as though fish are also inclined to do the same. While not real beds, most piscine forms are known to rest in a shelter, typically a coral or a crevice. They can be found resting in holes, caves, crevices, corals, within protective mucous layers, inside sponges, vegetation, buried in the sand, or (thanks to Finding Nemo) in anemones.

Physiology

As has been stated before, these marine creatures require nap just like the rest of us. And just like the rest of us, if they don’t get it enough in one go, they try to make up for it later on. Scientists have found that fish, like other animals, need sleep.  And if they are deprived of it one day, the nap “increases” the next day. This is known as homeostatic regulation. It was commonly observed among zebrafish. When the subjects were deprived of a nap for one day, the sleeping state the next day was much more intense, and the arousal threshold increased significantly.

No Bed? No Problem!

We can all agree on one thing: whatever the heck sleeping is, we all need it. But some animals would like to differ.

Take the tuna fish for example. Before it ended up on your dinner plate, it was probably doing better things. But proudly enough, slacking off was not one of them. Tuna fish, along with some sharks, have been observed to swim continuously and do not show any signs of sleep. They remain “awake” for the entire few hours of their life. The cause most likely would be their uneventful life. Their lives seem mostly boring (except for the part where you brutally murder them), and thus the function of snooze may prove useless.

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Underwater Slumber Party

While whales don’t technically count as fish, we felt like excluding them would be too mean. Whales have been observed by many biologists (and quite frequently some photographers too) sleeping in groups. One popular photograph (shown above) was taken by Stephan Granzotto and depicts the unusual sleeping pattern of sperm whales. Most whales and dolphins have been noted to nap in groups, and while it may not be the most exciting slumber party, it definitely increases the amount of safety.

Fish Living In Caves

A living organism dwelling inside a dark reclusive den and only ever hardly seeing the light of day. Does that sound familiar? Yup, you guessed it. While most introverts and crazy cat ladies can relate to this, there are certain fish that seek refuge in their own private confinement too. And the most intriguing bit about this? They require little to no nap. The cause is just as wild and mysterious as the fact.

In 2011, researchers sought to get to the bottom of cave fish’s sleeping habits. They were just as baffled as we were. They interbreed cave fish with surface fish and examined the offspring to see if the less sleep gene is genetic or not. Miraculously, the offspring creatures had almost the same habits as cave fish, thereby concluding that the awkward yet ideal sleeping patterns of these creatures are entirely hereditary. If only it were like that in humans. Sigh.

Don’t Forget To Breathe!

Breathing is easy. With little to no effort, humans and literally every other animal is able to breathe involuntarily. But for some giant water-dwellers, breathing can be more of a pain.

Humpback whales have been noted to be conscious breathers. Which means that they have to remember to breathe. Imagine that. Having to remind yourself to breathe every single second. We can already see you cringing. Unfortunately, humpback whales are only able to shut down half their brains, so the other half can be conscious enough to keep the breathing going. I know. A pain in the neck. But don’t feel too bad, because whales literally have nothing else to so with their lives! (We envy them)

Conclusion

While fish may not have the same sleeping pattern as most mammals, they definitely show signs of “resting”. These chubby little swimmers exhibit an impaired sense of touch and are known to be less reactive to arousal stimuli, such as shaking the container or screaming loudly into the bowl (though we highly discourage doing the latter).

All in all, fishes are just as tired at the end of the day as we are. So sleep tight little fishes! And don’t let the sea cucumbers bite!