How Do Clownfish Sleep? Upside Down?

Mar 12, 2022

How Do Clownfish Sleep?

When I first brought my Nemo home, I caught him floating upside down about halfway from the surface one day. Turns out he was just sleeping, but needless to say, it scared the daylights out of me. 

This happened in 2018 – and back then, I didn’t know how do clownfish sleep. But over the years, I’ve learned that clownfish are crazy fish with even crazier swimming styles. 

This blog will discuss how clownfish sleep and everything else related to it. It’s going to be a fun one. Buckle up! 

How Do Clownfish Sleep?

Most clownfish sleep at the bottom of the tank – hiding in anemones or inside hollow shells. However, they’re also known to sleep at the surface upside down or sideways, near the powerhead, or against the side of the tank. 

Most clownfish sleep in weird positions when first introduced to a new tank. And once they develop a symbiotic relationship with something (not necessarily anemone), they sleep close to it. 

If you thought your clownfish would lay down cozily in a corner and call it a night when it’s time to rest, you’re in for a surprise. 

Below, I have collected answers hobbyists left on different forums on how their clownfish sleep, and it’s nothing short of hilarious! 

Have a look. 

How Do Clownfish Sleep? Real Answers By Real People! 

Note: All the comments expressed below purely belong to the respective authors. 

“At night, my clownfish stay at the surface, floating on their sides. At first, I thought they were gone. But they just seem to sleep like that.”

“Mine sleep in their anemones.”

“I have had my pair of perculas for over 2 years now, and they always sleep right in the corner of the tank adjacent to the heater. They either sleep with tails up and heads down or vice versa.”

“My clownfish sleeps on top of a rock. Not sure if it’s a good thing.”

“My clowns bob up and down near the bottom corner of the tank. They look so strange.”

“They sleep laying on their sides at the bottom next to the slipper coral they host.”

“My fish sleep in the back corner in the cave. Sometimes they sleep separately, and sometimes they snuggle. When I first got them home, they slept at the top sideways. I thought they were dead.”

“I’ve had my clowns for 3 years. They sleep upside down next to each other halfway from the tank’s surface.”

“My clownfish sleep on the hairy mush like in a bed.”

“One prefers the corner glass, and the other nestles in the hammer coral.”

“I have some patches of hair algae growing on the back glass. My clownfish sleeps nestled in the hair algae.”

As you can see, no two answers are alike. Turns out clownfish really have weird preferences and styles when it comes to sleeping. 

And turns out, a lot of them like to sleep near the powerhead! Look at the answers I have curated for you below. 

“My clownfish pairs sleep near the powerhead.”

“My clownfish used to sleep in the corner near the powerhead. But I got them an anemone. And now they sleep in the anemone, all cuddled up.”

“My fish sleep in the top corner of the tank right next to the powerhead.”

“My tomato clownfish sleeps right behind the rock with his head up and tail down. He loves to be right in the flow of the powerhead.”

Recommended Readings!

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Percula VS Ocellaris Clownfish | Picture Guide

Freshwater Clownfish? Doppelgangers? Can Clownfish Live In Freshwater? 

A Clownfish’s Sleeping Behavior 

Yes, like all fish, clownfish don’t have eyelids. Therefore, they don’t close their eyes when asleep. Likewise, when we sleep, the neocortex region of our brains becomes passive. But fish don’t have neocortex at all. 

As evident from the comments above, we now know that they don’t sleep traditionally like us or our other pets. So, how do we know for sure that they sleep?

Let’s dissect their sleeping behavior in depth now! 

Although clownfish don’t sleep conventionally as most animals do, they will know that it’s time to call it a day when the night falls. They gradually become less responsive as their heartbeat rate and metabolism decrease. 

Truth be told, we’re still lacking in research when it comes to an understanding of what goes inside a fish’s brain when it’s asleep. 

But there are a few things we know for sure: 

  • Fish have sleep cycles
  • Their body produces hormones that regulate sleeping patterns
  • They have an internal clock like us 
  • Their heartbeat rate and metabolism slow down

And the following 4 criteria prove that clownfish sleep:

  • Typical resting posture in shelters 
  • Inactivity for extended periods 
  • High arousal threshold 
  • Alteration with activity in a 24-hour cycle

Now, let’s find out how to know when your clownfish is sleeping. 

5 Signs That Your Clownfish Is Sleeping 

Here are a few signs to look for to know if your clownfish is sleeping or not.

  • The fish takes a rest around the same time every day. 
  • The fish takes longer to respond to stimuli like food and light. 
  • The fish hasn’t really moved in a while. 
  • No eye movement can be detected. 
  • The respiratory functions are lowered.

Why Do Clownfish Sleep? 

Clownfish sleep for the same reasons rest of the creatures in the animal kingdom sleep. To generalize, the reasons why clownfish sleep can be divided into 2 categories: adaptive sleep hypothesis and restorative sleep hypothesis. 

Adaptive Sleep Hypothesis 

The adaptive sleep hypothesis states that any living being sleeps to better adapt to its environment. For example, sleeping when it’s dark helps animals avoid potentially dangerous scenarios like confronting a predator. 

Restorative Sleep Hypothesis

According to the restorative sleep hypothesis, any living being sleeps to help its body recuperate. That’s because when asleep, a body has the chance to repair itself, process new information and memories, and enhance immunity. 

Do Clownfish Have Circadian Rhythm?

Circadian rhythm refers to the 24-hour cycle that’s part of the body’s internal clock. Just like us, clownfish, too, have a circadian rhythm. Therefore, they have a standard sleep-wake cycle that is pretty comparable to ours. 

According to a study published by Stanford University, fish secrete hormones that drive their sleeping pattern and calibrate their internal clocks.

Therefore, your clownfish experience the following when the lights go off at night:

  • Their metabolism starts to slow down 
  • Their cardiac functions are lowered 
  • Respiration is lowered 
  • The brain will produce melatonin hormone 
  • Fins and tail flap very subtly to maintain the sleeping position

Can Clownfish Sleep Without Anemones Present In The Tank?

Almost every clownfish has a symbiotic relationship with an anemone in the wild. Therefore, it sleeps among the anemone’s stingy tentacles. However, in captivity, a clownfish doesn’t necessarily need to have an anemone present with it to fall asleep. 

If there’s an anemone present in the tank, the fish will prefer sleeping inside it most definitely. However, they can sleep perfectly fine without it too. 

In the absence of anemones, clownfish adopt a ‘pseudo anemone,’ like a hollow shell or an empty coral, as its host and sleeps inside/around it. 

Although raising clownfish isn’t challenging, the same cannot be said about housing anemones. The latter demands more time, investment, and elbow grease. 

Anemones are definitely not everyone’s cup of tea. But don’t worry – your clownfish will sleep soundly in the absence of anemone as well. 

5 Tips To Help Your Clownfish Sleep At Night 

Do not feed your clownfish right before bedtime. If you do, they will feel energized and remain active through the night. 

Ensure the water parameters are stable and nothing evil is brewing inside the tank. 

Don’t keep your clownfish alongside large and aggressive species. Your clownfish can’t sleep well if it’s living in constant fear. 

Turn off the tank’s and the room’s lights at night. 

Place your clownfish tank in a peaceful place that doesn’t receive a lot of footfall, light, and noise. 

Can Clownfish Suffer From Sleep Disorder?

Sadly, no research yet has been carried out to study whether clownfish suffer from sleep disorders or not. However, a study conducted on zebra danios showed that the fish suffered from sleep disorders when sleep deprived. Thus, we can assume that the same happens with clownfish too. 

In the experiment, zebra danios were first deprived of sleep for a few days with the help of a mild electrical current. Later, the fish slept for longer durations when they were allowed to have a regular day and night cycle without any disturbances. 

The Two Stages Of Clownfish’s Sleep 

An average human’s sleep cycle consists of 4 stages – 1 stage of slow-wave deep sleep, 2 stages of light sleep, and 1 last stage of rapid eye movement. 

Even though clownfish do not have a neocortex as we do, studies have shown that fish experience at least two sleep stages: REM and slow-wave sleep. 

Recommended Readings!

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Do Cichlids Sleep? Can They See In The Dark?

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Frequently Asked Questions 

Before we end this article, here’s a quick look at the frequently asked questions on sleep and beyond. 

Do Clownfish Sleep On Sand?

Yes, clownfish that prefer sleeping at the bottom sleep on the sand. It’s normal behavior. Sand is naturally cushioned and hence plushy. Therefore, clownfish often resort to sleeping on the sand. 

Do Clownfish Sleep At The Bottom Of The Tank?

Yes, most clownfish sleep at the bottom of the tank – but it’s not always the case. As you saw in the answers shared above, a good number of clownfish prefer floating on the surface or midway vertically or horizontally to sleep. 

How Many Hours Do Clownfish Sleep?

Just like us, clownfish are diurnal creatures. Therefore, they sleep for anywhere between 8-12 hours each day. When the night creeps in, their mind and body automatically prepare to fall asleep. 

And by the way, if your clownfish is deprived of sleeping as much as it wants or needs, it will feel groggy and irritable the next day. 

Do Clownfish Take Naps?

Yes, clownfish are known to take naps if they need to. Especially if they didn’t get enough rest the previous night, they would compensate for it through quick naps throughout the day. 

Do Clownfish Sleep In Anemone? How Do Clownfish Sleep In Anemone?

Even though clownfish can sleep at the base of the tank or inside shells and caves, if there’s an anemone present in the tank, they strongly prefer sleeping inside the anemone. At night, they snuggle deeply within its stinging tentacles. 

As you already know, clownfish are immune to anemones’ tentacles, thanks to a particular mucus layer they produce. 

Do Clownfish Ever Stop Swimming?

It’s interesting to note that clownfish don’t stop swimming even when asleep. This is because they have very soft pectoral fins, and they cannot perch on them as most fish do. 

Therefore, a clownfish needs to subtly move its fins and tail to hover above the chosen spot even while sleeping. 

Do Clownfish Swim While Sleeping? 

Yes, clownfish swim while sleeping. However, they swim very subtly to hover above the selected swimming spot. They don’t cover the distance. They gently move their fins and tails to stay afloat. 

How Long Should You Leave The Lights On For Clownfish? 

You should not leave the lights on for any longer than 8 hours a day for your clownfish. If you keep lights on for longer than that, there’s a good chance that it will impact your fish’s sleep routine. 

Plus, 8 hours of light per day is enough for most aquatic plants. So you don’t have to worry about that. 

Where Do Clownfish Sleep In The Ocean?

In the ocean, all clownfish share a symbiotic relationship with anemones. Therefore, they sleep safely inside their stinging tentacles. Anemones protect clownfish from potential predators at night. 

In return, clownfish provide nourishment, help them breathe, and chase away predators like butterflyfish that snack on anemones.

Is It Normal For Clownfish To Lay Down?

Yes, it’s perfectly normal for clownfish to lay down at the bottom from time to time. They do so to sleep, rest, or maybe even contemplate (who knows, right?). 

However, if you find your clownfish laying at the bottom more than usual, it could be an ominous sign. For instance, the water temperature is too hot for the fish’s liking – therefore, it has resorted to staying at the bottom where the water is relatively cool. 

Besides that, some other reasons behind a clownfish laying down could be disease, poisoning, wrong water parameters, and stress. 

If you find your fish retreating to the base more often than not, try to gradually experiment with the tank’s environment and the fish’s diet until you find out what’s the real problem. 

Are Clownfish Happy Alone?

Unfortunately, we’re not very good at understanding a fish’s behaviors and feelings. So, we wouldn’t really know if they’re happy or sad when kept alone. But the general practice is to at least keep 2 of them in the same tank since these fish live in social groups in the wild. 

Many hobbyists report that the fish becomes considerably more active when kept in pairs or groups. So, that might be a strong indication that they long for a companion in captivity.

Final Words: How Do Clownfish Sleep?

There’s no one particular answer to how clownfish sleep. While some sleep quietly at the base, others like to hang upside down at the surface during slumber. Even more, some rest on top of powerheads. 

But if there’s an anemone present, they’ll sleep inside it. 

I rummaged through a dozen different forums to see if there’s one common explanation or at least a pattern to answer this question. But guess what? I was met with a different answer each time! 

Irrespective of how your clownfish sleep, it’s critical to understand that these fish, too, have a proper sleep cycle and a circadian rhythm. Thus, you need to ensure they get at least 8-10 hours of undisturbed sleep every night. 

Recommended Readings!

Clownfish And Blue Tang | Here’s Why It Won’t Work 

What Kind Of Fish Is Dory? Why They’d Make Terrible Pets?

Can You Eat Clownfish? Here’s Why You Wouldn’t! 

rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.