Do Clownfish Sleep? (Sleeping Behavior Explained)

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As a fish owner, I was really interested to know whether or not clownfish sleep. Since they don’t have eyelids, it was difficult for me to tell if they behave like humans during nighttime. More importantly, I wanted to distinguish between typical sleeping patterns and ongoing diseases.

Yes, clownfish do sleep, especially during nighttime. At this point, they will lay motionlessly at the bottom of the tanks and will be difficult to arouse. Clownfish may also sleep inside anemones, hovering without any significant movement. That allows them to stay out of predators’ sight.

As we move forward in this article, I will elaborate on the typical behavior of clownfish present during their sleep. Also, I will show you how to distinguish between sleepiness behavior and impaired health conditions.

Also Read: Clownfish Care Guide

Can Clownfish Sleep?

The common belief is that most, if not all, animals sleep, and they do so at regular intervals. You can tell that an animal is sleeping because it will have its eyes closed. It may also find a comfortable spot and lie down. During this period, a portion of its brain will shut down.^[1]

However, clownfish are not like ordinary animals. As their name suggests, they are fish. They live in the water. To be more specific, they hover. Do they also lie down when they sleep? And if they do, what about their eyes? Do they close them during this period of rest?

These are the questions that will burden new clownfish owners. That is particularly interesting because clownfish, and many other fish, are different than what we are used to. Fortunately, these questions have plenty of straightforward answers.

Yes, clownfish do sleep. This is a trait they share with most other fish. They have regular periods during which they rest. You probably won’t know this unless you have taken the time to observe your fish, especially at night.

Actually, some of you have probably seen your clownfish sleep. However, you could have presumed that they had simply zoned out or entered some sort of trance because they appeared to float in place for long periods.

Regardless of whether or not you have seen them, there no doubts are surrounding this issue. The scientific community agrees that clownfish sleep. In fact, a few scientists argue that almost all fish sleep.^[2]

Still, clownfish don’t sleep like regular people. As was mentioned above, they live in water. So, they can’t just lie on their side. Or rather, they can, but some of them don’t. Clownfish also lack eyelids.^[3] So, they can’t be expected to close their eyes. In that regard, one might wonder how anyone can even tell that fish are sleeping.

Is it possible that scientists and fish owners have mistaken specific behavior in clownfish for sleep? To understand the answer to that question, you must first understand the definition of sleep.

For particular behavior in animals to be formally recognized as sleep, there are specific criteria that it must meet:^[4]

First of all, the animals in question must maintain a specific posture. You see this in humans who typically lie down when they sleep.

The animals must also slow down or enter a maintained state of inactivity. You also see this in humans. Not only do they lie down, but they become inactive.

Additionally, the animals in question will become challenging to rouse. To wake a sleeping person, you have to nudge and prod them.

Lastly, the state should be reversible.

You can see all these signs in clownfish. Yes, they are going to keep their eyes open when they sleep. But they will also become inactive. If you take a closer look, you will see that they answer each one of these criteria, especially when their lights are off.

Still, do not expect all the fish in your aquarium to exhibit similar behavior. While some fish will stop moving altogether, others will simply move slower. They are sleeping all the same, but they need to remain in motion to keep their gills ventilated.

In this state, their breathing will reduce along with their metabolic rates. If you were to study their bodies, you would also observe lower brain activity.

Clownfish Sleeping Behavior (And Locations)

The fact that some fish remain in constant motion is a source of confusion for amateur fish owners who cannot help but conclude that their fish are awake but simply entranced. It takes them a while to learn to read the signs.

The best way to determine whether your clownfish is truly asleep or merely swimming slowly is to add some stimuli to the tank. Don’t startle the fish. Do something that would typically draw the creature’s attention. One option is to add food to the tank. If your clownfish doesn’t respond even though its eyes are open, then it is asleep.

Of course, some diseases will make your clownfish lethargic. You shouldn’t always presume that your fish’s inability to respond to stimuli is a sign of sleep. Look for patterns. If the creature shows the same level of inactivity during the same period each day, it is merely sleeping.

You should also test your clownfish’s appearance. Look for white dots or ripped fins. One of those may suggest that your fish are sick rather than sleeping. However, if they look perfectly fine, that should raise your suspicions that they are presenting a physiological behavior.

There should also be periods during which your fish is active and responsive. Otherwise, if it is continuously sluggish, it is probably diseased. If it has remained entirely inactive for hours on end, you might have a dead fish on your hands.

As with humans, fish have a point in the day or night when they finally wake up. They do not stay asleep indefinitely. This might sound obvious, but you might be surprised by the number of fish owners who had dead fish in their tanks for days without realizing it.

Sleep is a complicated undertaking for fish in the wild. They are quite vulnerable to attack, which is why some of them must remain on high alert. They have to be ready to make a quick escape the moment a predator enters their vicinity. Of course, this isn’t an issue in an aquarium, not unless you have surrounded your clownfish with dangerous tank mates.

Not all fish sleep the same way.^[5] Some will lie down at the bottom of the tank. You have probably seen this in your clownfish. This behavior is the most frightening for amateurs because fish that are lying down at the bottom look like they are dead.

Other fish are not content to simply lie on top of the substrate. They will find something to burrow into. Quite a few will remain afloat, drifting slowly through the water. These are the ones that look like they are entranced rather than sleeping. They are also the least alarming because they don’t look dead.

Here is a YouTube video of a sleeping clownfish. As you can see, their typical sleeping behavior is to be motionless at the bottom of the tank. Sometimes they will lay inside anemones. However, as in this case, they may be lying on a rock or gravel.

Why do Clownfish Sleep?

Like humans, clownfish need sleep to maintain their health. They use that period of inactivity to rejuvenate their bodies and organs. It is a therapeutic process, one that resets their system. However, don’t expect clownfish to experience REM sleep like humans.

Their brains are not that complex. But they still need their sleep. Some scientists performed a study in 2007 in which they deprived a group of zebrafish of sleep by interrupting their usual 6-hour nap.^[6]

Not only were the zebrafish resistant to attempts to wake them the next day, but the movement of their mouth and gills was sluggish. It was clear to the researchers that the sleep deficit was slightly debilitating the creatures’ ability to function during the day.

As such, it is generally accepted that sleep is as essential to fish as it is to other animals. The lack of sleep does not harm clownfish as drastically as it does humans, but they still need it.

When do Clownfish Sleep?

Most people associate sleep with nighttime and darkness. The average human being sleeps at night. Most animals are the same, fish included. Nevertheless, some species are nocturnal. These will sleep during the day and become active at night.

Nocturnal fish are challenging to keep, especially if they are so much larger than their tankmates. They might be tempted to make an easy meal out of the sleeping fish in their tank. Luckily, clownfish are not nocturnal. Just like humans, they tend to sleep during nighttime.

They swim, hunt, and mate during the day. Once the sun sets, they become inactive and unresponsive. It is also during this period that they sink to the bottom of the tank in search of darkness.

That behavior could also happen during the day if your tank is located in a shady area. The clownfish’s inner clock could be manipulated when it is out of its natural habitat. However, domestic lives would have an impact on their health. That is why I suggest imitating the conditions outside.

Like humans, fish use the presence and absence of light to demarcate the boundaries between sleep and wakefulness. In the wild, they remain active when the sun is up, and they sleep once it sets.

In the tank, if you keep the lights on all day and night, your clownfish will stay awake consistently. Can fish sleep when the LEDs are on? Yes, they can. However, the light stimulates them.

They are more likely to stay awake than they are to fall asleep. But this is not good for their health.^[7] This is why new fish owners are encouraged to create a stable daytime/nighttime routine for their tanks using automated lights.

You need to ensure that your tank gets 12 hours of light and 12 hours of darkness. This will mimic the day/night cycle clownfish encounter in the wild. It will also encourage them to create a stable schedule for their sleep.

Some think that it is cheaper to rely on natural light to meet the needs of their tank. But natural light is not consistent. It will fluctuate based on the weather conditions, the location of the aquarium in the room, and the presence of obstructions in the vicinity.

You can’t rely on the room’s artificial lighting either, because it is equally unreliable. What happens when you forget to switch the light on? A lot of people sleep earlier on some days than others, and wake up later on some days than others.

These delays are going to impact the time that the artificial lighting in the room is switched on and off, and that will create instability in your fish’s sleep cycle. If you want your clownfish to develop a healthy sleep schedule, get an aquarium light with a timer.

Program it to activate and deactivate consistently every day. Also, you should add some plants to the tank to give your fish some privacy whenever it falls asleep. The most suitable one is the anemone. If you are interested, here is an article where I discussed which anemones will work best with each type of clownfish.

Conclusions

Like humans and other kinds of fish, clownfish do sleep. The typical behavior they present is lying motionlessly at the bottom or inside anemones. The ideal time for them to do so is at night. Therefore, I encouraged you to mimic the outdoor lightning hours inside your tank.

However, if your clownfish are floating sideways, that means trouble. At this point, I suggest that you scrutinize your fish. Look for white spots or ripped fins that may indicate your clownfish are sick.

I hope my article has answered your question regarding whether or not clownfish sleep. As you will raise them longer, I’m sure you’ll learn to distinguish typical sleepiness from ongoing diseases. Either way, if you feel hesitant, feel free to consult a local pet fish owner.

Can Clownfish Sleep?

Clownfish Sleeping Behavior (And Locations)

Why do Clownfish Sleep?

When do Clownfish Sleep?

Conclusions

References