Do Angelfish Sleep? (Signs, Sleeping Habits & More)

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So many times, I’ve seen my angelfish float motionless across its tank. That immediately popped the inevitable question – do angelfish sleep? Or should I be worried my fish doesn’t feel well? That was when I began to research the angelfish sleeping habits. Actually, what I found quite surprised me.

Angelfish do sleep since, during the night, their mobility is reduced, and they become less active. As proof, their stripes fade, and they motionlessly stick to the bottom of the tank. However, unlike humans, they do not become unconscious nor experience REM sleep.

However, sometimes, an immobile angelfish might indicate a problem. You should also get familiar with how to manage your fish’s light hours and how it might affect them. In some cases, you might find that sudden light changes could have an impact on the fish’s metabolism. Keep on reading to understand your fish’s sleeping habits once and for all.

Also Read: Facts About Angelfish

Are Angelfish Capable of Sleeping?

To determine whether or not Angelfish sleep, you need first to figure out whether or not sleep is an activity in which fish, in general, indulge. Scientists believe that the majority of animals experience sleep.[1]

However, the way they sleep will vary. Some will sit, while others will lie down. Some animals are also quite happy to sleep while standing – for instance, the giraffe.

In the case of fish, it is presumed that most of them sleep. But sleep in fish is not precisely the same as sleep in people. When a person falls asleep, some form of loss of consciousness occurs. Their bodily functions slow. This allows the mind to rest, refreshing its memory circuits.

This is somewhat similar to what happens with fish. There is always a point in the day or night during which fish become either slower or immobile. If you have them in a tank, you will notice that they no longer respond to stimuli. And if they do, they are quite slow.

This is taken as proof that fish sleep. This activity is easy enough to observe, not only in the wild but in any tank. Because fish always have a moment in the daytime or at night during which they are inactive (and because this happens regularly), people have concluded that fish must sleep.

How do Angelfish Sleep?

The physical sleeping habits of fish will depend on the species. Some dig into whatever they can find at the bottom of their water body, be it sand, rocks, or plant life. Others simply hover near the bottom, mostly immobile, showing little to no signs of life.[2]

Herring is just motionless in the water, whereas bass prefers to rest under logs. Out in the wild, fish will find crevices and pockets to hide in while they sleep. If all you have is a tank, your fish will probably hover near the bottom. At least this is what I find my angelfish do during night time. 

How Can You Tell That Your Angelfish Is Sleeping?

First of all, you need to understand what a sleeping angelfish looks like. Angelfish are brightly colored fish with vertical bands of a darker color. These bands are protective. The angelfish use them to blend into their surroundings where necessary.

As a starting point, It should be noted that this species has the power to turn these bands on and off. If you turn the lights off and you leave, once the angelfish falls asleep, it will drift to the bottom of the tank, becoming motionless. More to the point, it will lose the color in its body, even in the bands.[3]

If you wake the fish by turning the lights on, it will not only startle back to life, rising from the bottom of the tank, but the color in its bands and body will return.

Now, this is where some scientists argue that the fish was merely inactive; that it was only in a state of reduced metabolism for rejuvenation purposes.

Ultimately, you will find an even more significant number of voices pushing the idea that the angelfish is actually sleeping whenever you find that it is lying motionless at the bottom, the color leeched out of its body.

Is a Motionless Angelfish Always Asleep?

Plenty of people have descended into a panic because they came home to find their angelfish lying motionless at the bottom of the tank. But that raises several questions. Assuming that they not dead, are every motionless angelfish asleep?

Well, it should be noted that, like other fish, some angelfish will remain in motion even when asleep; though, that motion usually is lethargic.

That being said, it has been suggested that fish tend to become disoriented in the dark. This is especially true for angelfish in tanks in homes where you keep switching the light off whenever you leave.

Out in the open water, changes in the light occur, but they are slow and gradual. When the light is suddenly turned off, and the angelfish is plunged into unexpected darkness, it can become disoriented. As a result, it will float slowly and aimlessly in one direction or simply rest on the floor.

But once the light comes back on, it will come to life and resume its regular activity. For this reason, you are encouraged to coordinate the order by which lights go on and off.

There should be an interval of a few minutes to allow the angelfish to acclimate. However, this isn’t a cause for concern. The disorientation won’t harm your fish.

An Angelfish that has sunk to the bottom of the tank might be sleeping. But it could also have a swim bladder disorder, which is a severe issue that could affect its buoyancy.[4] If you lack certainty on this matter, consult an expert. 

What is Happening While The Angelfish Is Asleep?

There are a few things that you should keep in mind about the way fish sleep:[5]

  • First of all, it should be noted that many fish actually sleep at night. Some are nocturnal. But plenty of species prefer to remain active during the day and then sleep at night. 
  • Secondly, fish do not follow the typical circadian rhythm. For instance, they do not experience REM sleep. Most dreams happen during REM. So that should squash any ideas you might have about fish potentially dreaming. 
  • Thirdly, in the case of angelfish, their eyes remain open even when they are asleep. This is true for most fish. 

When angelfish sleep, their metabolism reduces significantly. This is one of the reasons why they become inactive. However, fish are not precisely unconscious, not in the same way as humans.

Your angelfish, especially if they are in the wild, know that they have to keep an eye out for danger. In other words, even when asleep, they are still alert.

This is particularly important for angelfish because they have aggressive tendencies. These creatures can appear docile when you first introduce them to a tank.

But under the wrong conditions, their violent trends will emerge, driving them to attack other fish. In some cases, they will even consume their own babies.

This can happen when they feel stressed and threatened; when they have young ones to protect and in cases where the tank is too small.

The fact that they can grow large enough to eat smaller fish makes them a problem. However, Angelfish will also attack one another. So you can see why they would need to stay alert even when sleeping.

Also Read: Can Angelfish Live Alone?

Why Do Some Fish Keep Moving Even When They Are Sleeping?

As was mentioned above, fish do not sleep like people. They do not always lie in one place and stay there throughout the night. They need to ensure that water is continuously flowing over their gills. This is what keeps their bodies supplied with oxygen.

This is why you will notice that sharks keep swimming even when they are sleeping, though they are much slower. 

What About Fish That Need to Migrate?

When fish are migrating, you will notice that they swim continuously for long periods. Does that mean that they don’t sleep? Well, actually they do. As was mentioned above, fish can keep moving even when they are asleep. 

In the case of migratory fish, the fact that they are moving in a school means that their need for visual sensory information is reduced. As such, they can enter into a sleep-like state in which their visual input is reduced, but they are still swimming alongside the other fishes.

It has also been argued that, in some cases, fish adjust their sleeping patterns when they are on the move, choosing to forego sleep for the duration of their journey.[6]

How do People Perceive Angelfish Sleeping Habits?

Angelfish are among the most popular fish in any aquarium you might visit. They stand out because of their multi-colored bodies. Though, some have argued that the multi-colored saltwater fish from the tropics are only angelfish in nicknames.

They state that ‘Angelfish’ can only accurately refer to the freshwater variety.

But that isn’t an issue that concerns most aquarium owners. Why should they care that their angelfish probably originate from P. eimekei or a scalare hybrid? In fact, most angelfish owners are primarily concerned with the feeding and mating habits of these creatures.

And once those are taken care of, you will find them debating their sleeping habits, a topic that fascinates even those people that do not own fish.

They cannot help but wonder whether angelfish sleep. They might be surprised to learn that others have asked that question before and endeavored to answer it.

Also Read: Do Angelfish Recognize Their Owners?


The simple answer is ‘Yes.’ Angelfish do sleep. The complicated answer is this: no one knows for sure. Some scientists have chosen to take the inactivity of angelfish at night as a sign that they are sleeping.

Others have argued that this inactivity could have all manner of causes. Ultimately, there is no definitive proof that angelfish sleep. But there is also no conclusive proof that they do not.

The consensus is that angelfish probably sleep. Either way, it is both essential and exciting to get more familiar with the topic. I certainly hope my article has achieved that goal.