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Do Angelfish Sleep? (And Are They Diurnal or Nocturnal?)

Do Angelfish Sleep? (And Are They Diurnal or Nocturnal?)

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This post is written to the author's best knowledge and is not intended to be used in place of veterinary advice. In addition, this post may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.

Observing angelfish is something that can be quite satisfying. The angelfish in your aquarium are very pretty, and watching them swim around will be relaxing.

You likely enjoy spending time watching the tank, but you don’t observe the tank at all times. It’s very likely that you don’t see what the fish get up to while you’re sleeping at night.

This could lead you to wonder whether angelfish sleep or not. Do these fish go to sleep during the night or is that simply not something that fish do?

Keep reading to learn about whether angelfish sleep. You’ll have a much better idea of what the angelfish are doing at night once you read the information below.

Angelfish Do Sleep

To answer the question simply, yes, angelfish do indeed sleep at night. If you ever get the chance to observe angelfish at night, then you’ll see that they sleep at the bottom of the tank.

During this period of time, the angelfish will be in a resting state. You’ll see the colors of the angelfish fade, and they will generally lie motionless somewhere at the bottom of the tank.

Some angelfish might choose to sleep right on the substrate while others will possibly sleep near hiding spots on the bottom of the tank. This is totally normal for the angelfish, and you don’t need to worry if you come across the fish and see it sleeping.

This doesn’t mean that angelfish sleep in a traditional sense, though. Just like how angelfish don’t yawn like humans, the way that fish sleep is quite different from how humans sleep.

Regardless, it’s considered by many to be a form of sleep. There really isn’t a better way to describe what the angelfish are doing.

They need to rest, and this is the period of time that they do it. The angelfish will spend time resting this way at night so that they can have the energy to do what they need to do during the day.

Are Angelfish Diurnal or Nocturnal?

Angelfish are diurnal fish, and this means that they sleep during the night. When the light starts to fade, you’ll see that angelfish will go toward the bottom of the aquarium and find resting spots.

In the wild, this is pretty much what they do, but they’ll be resting in different locations. When you see angelfish sleeping in the wild, they’ll be hiding among the various crevices of the reef.

These fish don’t go too deep into the water when in the wild either. They generally don’t go deeper than fifty meters.

Nocturnal fish are completely different from this. They are active during the nighttime, and they choose to find resting spots during the day.

Can Nocturnal and Diurnal Fish Be Kept in the Same Fish Tank?

It is possible to keep both nocturnal and diurnal fish in the same fish tank. You just have to be careful how you go about doing it.

Of course, you need to make sure that the fish are compatible before moving forward. Incompatible fish might wind up attacking each other or even eating each other.

Angelfish are known to be semi-aggressive fish. They will certainly eat fish that are small enough, and they’ve also been known to bully some types of fish.

They can also be bullied by bigger and more aggressive fish. You need to be careful about the types of fish that you put in the tank with the angelfish.

There should be some nocturnal fish that will be compatible with angelfish. You’ll just need to do a bit of research to choose which fish you want to go with.

You also won’t want to keep lights on at night that will disturb the angelfish. Otherwise, it would mess up the sleep cycle of all of the diurnal fish in the tank.

Thankfully, there are lights out there that don’t pose a problem. You can purchase what are known as “moonlights” for your aquarium.

These types of lights are fantastic for when you want to be able to see your fish at night. They’re very gentle lights that won’t disturb the fish.

It’ll be enough to help the nocturnal fish to see when they’re active at night. The angelfish should still be able to sleep just fine as well.

How Angelfish Sleep Differs From Human Sleep

You might be curious to learn a bit about how angelfish sleep differs from human sleep. When you go to sleep at night, you’re going to enter a state of deep sleep.

Angelfish never go into a deep sleep state. They remain in a resting state, but they’re very alert during this period of time.

The angelfish will be able to react to things that are going on around them. They need to remain alert so that they swim away or defend themselves against attacks.

So angelfish never actually experience REM sleep. The way that they sleep is simply different from what you understand as sleep.

Humans sleep much more deeply than fish do. A human isn’t nearly as alert as an angelfish during the night.

Angelfish don’t experience a loss of consciousness when they’re sleeping. To some, this means that they don’t sleep in a traditional sense.

The truth is that it doesn’t matter whether they’re technically sleeping or not. What they’re doing can either be considered sleep or you can consider it some form of resting.

There are examples of land animals who can remain alert while sleeping, though. For instance, deer can sleep in the woods, but they can remain very aware of their surroundings.

This allows the deer to react to predators and other things that might try to sneak up on it. It’s extremely difficult to sneak up on a deer, and it’s likely not something you should try to do.

What Happens While an Angelfish Sleeps?

So what is it that happens while an angelfish sleeps? What is going on with the angelfish during this time?

One of the major things that you should know is that angelfish have their metabolism significantly reduced when they’re in a sleeping state. This is actually considered to be one of the major reasons why they enter a sleep state.

It could be a good way for them to conserve energy since they have to compete for resources in the wild. They need to do this for the sake of survival.

In your fish tank, it might not be as necessary, but it’s still healthy for the fish to have a natural cycle. You should endeavor to give the fish a natural day and night cycle to the best of your ability.

If you ever see your fish sleeping, then you’ll notice that they sleep with their eyes open. This is completely normal and you don’t need to worry that something might be wrong with the fish.

Fish don’t have eyelids, after all. If you’re not that familiar with caring for fish yet, it can still be weird to see them sleeping with their eyes open.

You’ll be able to observe them if you install the moonlights that were mentioned earlier. Just don’t try to turn normal lights on or this will scare the fish and disturb their sleep.

It’s also interesting to note that fish sometimes move when they’re sleeping. This is because fish need to keep water moving over their gills continuously so that they can breathe.

You might notice an angelfish move from one spot to another from time to time at night. There will likely be times when the angelfish is motionless as well, but this won’t be for the entire night.

Ensure That You Have a Big Enough Fish Tank

Ensuring that you have a big enough fish tank is going to be important when you’re caring for angelfish. As mentioned earlier, angelfish are a semi-aggressive type of fish.

They can become territorial, and it wouldn’t be unusual to see angelfish fighting other fish. An angelfish will sometimes choose to fight fish over territory.

This can become a real problem if you’re trying to keep the fish in a small tank. A community tank that is packed with too many fish will cause the fish to experience stress.

Stress is very bad for the angelfish, and it can lead to various health issues. When an angelfish is stressed, it’ll wind up having a weakened immune system.

Having immune system problems will make the angelfish susceptible to infections. You don’t want bad things such as this to happen to your pet fish.

A crowded fish tank could also make it very difficult for the fish to sleep properly. There might be fish that won’t feel as if they can find a comfortable and safe spot to sleep.

It’s fine to want to keep many fish in a community tank, but you need to be reasonable. Try to pick out a fish tank that is large enough for all of the fish that you wish to keep in it.

As a general rule, it’ll be better to go with a larger tank. Angelfish will appreciate having more space.

Remember to pick out the fish carefully as well. Even if you do have a large tank, angelfish will fight and bully other fish if you don’t pick compatible fish.

Angelfish can also fight each other. Male angelfish don’t get along well, and this is especially true when they’re placed in small tanks.

If you wish for the angelfish to be able to sleep peacefully at night, then give them a large tank. Make sure that you have enough room in your house for a decently sized aquarium.

Otherwise, it’ll be fine to use a slightly smaller one so long as you don’t put too many fish in the tank. You might want to stick to using a 55-gallon tank or larger when caring for angelfish, though.

Give the Angelfish Hiding Spots

You should really consider giving the angelfish hiding spots that they can utilize. This is likely going to help the fish to feel more comfortable during the night.

When you find angelfish in the wild, they’re going to utilize plants and hiding spots such as crevices in the coral reef. If you can make it so that the fish tank replicates this, then they will be much more at ease.

Some fish might feel much more comfortable if they’re able to sleep in some type of hiding spot. It gives them some level of security so that they can rest.

Angelfish might feel more stressed than usual if you don’t put aquatic plants in the tank. Not only do these plants make your tank look nicer, but they also help your fish to feel better about the environment.

There are many types of aquatic plants that angelfish enjoy. Amazon Sword plants have proven to be particularly popular.

Jungle Vallisneria (often shortened to Jungle Val) will be another stellar option. You can easily get live plants for your aquarium at the pet store, but you’ll also be able to order what you need online.

Rocks and reef decorations can also work pretty nicely to give the fish hiding spots. However, you shouldn’t use these as replacements for live plants.

It’s truly not going to be a complete angelfish tank unless you have plants in there. They’ll help the angelfish to sleep better, and they’ll make them feel much less stressed overall.

Final Thoughts

You’ve been able to learn quite a bit about angelfish and how they sleep. While it is technically debatable whether what angelfish do at night can be considered sleeping, it’s easier to just say that they sleep.

Angelfish enter a resting state at night even though they remain alert. They don’t ever lose consciousness during this time, and they certainly never experience REM sleep.

They need to remain alert so that they can respond to potential threats. It’s normal for fish to sleep in this fashion.

Angelfish in your fish tank will sleep at the bottom of the tank. They might sleep directly in the substrate or they could look to sleep in some type of hiding spot.

In the wild, angelfish often sleep in the crevices of the reef. In your fish tank, they might sleep hiding among the plants that are at the bottom of the aquarium.

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