Do Fish Need Darkness To Sleep? 5 Things You Must Know!

It is an interesting question: do fish need darkness to sleep? Fish are nocturnal creatures, which means they do not sleep at all during the day. They do however require a lot of relaxation or to be healthy. 

This article is about how many hours do fish need darkness? Do fish prefer light or dark in the aquarium? What do fish do at night? Can fish sleep with room lights on? Can fish sleep with blue lights on?

Do Fish Need Darkness To Sleep?

To answer the question, first, it is important to know do fish sleep? So that we know darkness plays any role in their sleep cycle or not? If you know the answer let’s move forward, If not then please read the mentioned article to get the answer more precisely. 

Fish do not need darkness to sleep. Fish do not have eyelids, so they do not necessarily have “sleep” in the same way humans do. They do however require periods of lowered activity to rest and recuperate, which is known as a “sleep-like state.” 

At least many fish do not need darkness to doze off for the day. Put another way, a fish doesn’t need to have complete darkness in order to feel comfortable enough to doze off at night. Fish sleep with the lights on!

People do not need complete darkness to doze off, do they? However, if you do leave your aquarium lights on while the fish are sleeping it may cause them stress. Fluorescent lights do not emit much heat and will therefore not raise the water temperature of a tank or bowl more than about one degree Fahrenheit (0.6 degrees Celsius). If possible, do your best to aim your aquarium lights so that they do not shine directly into the fish tanks at night.

How Many Hours Of Darkness Do Fish Need?

There is no set amount of hours that fish should sleep for. Some do need darkness to sleep, but not all do. However, some do have their own sleeping preferences, so it is important to research what your specific kind of fish needs.

As long as you are providing a safe environment for them to live in – one without predators or other life-threatening hazards – it’s important to do what you can to make them feel comfortable and safe in their surroundings. This means keeping lights low, and not disturbing their sleep by playing loud music or making too much noise around the tank at night time.

Some fish do prefer light over darkness; however, many do sleep better in a dark environment.

What Do Fish Do At Night?

Fish are active during the day. Fish do not sleep as we do but take rest. During this period, fish do not move much and do not eat as well. They do not have eyelids to close their eyes tightly as other animals do. So they rely on darkness for a good night’s sleep as it provides them with a soothing effect to help them doze off.

Notably, do fish need darkness to sleep? Yes, they do.

It is not an uncommon sight for people to see their fish dozing in the dark. Some examples of fish that do this are lionfish, sharks, and rays. It can be inferred from this observation that it must be normal for fish to sleep at night.

However, do not leave your fish tank in complete darkness or else your fish will die. Fish do need light so do not think of putting them in a pitch-black environment unless you want to turn the situation into an aquarium nightmare.

How Many Hours Do Fish Sleep?

Fish do not need a block of hours to sleep. When you go to bed at night do you doze off for a few minutes and wake up? This is exactly how fish sleep.

Fish do not have eyelids for sleeping, so they do not “close their eyes” as we understand it. Fish do take rest periods during which they do not move, do not eat, do not grow, do not do anything except breathe. How long these periods depending on the species of fish. It depends on the environment, and it depends on how well they are taken care of.

Many fish do get more sleep than others do. Fish do not sleep as humans do. A human usually sleeps for hours at a time, sometimes up to 8 hours. A fish will doze off, rest its muscles and allow itself to do some very basic tasks, but do very little else. Fish do not dream as humans do, they do not have a huge variety of brain waves when sleeping. For the most part, fish sleep is really only rest periods between activities.

Fish need at least 3 minutes to rest each hour in order for their gills to do basic functions such as breathing. They do not do anything else during rest periods, they do not eat and do not do much as far as moving around.

Also, we have a complete article on this: How many hours do fish sleep? The exact numbers!

When Do Fish Sleep?

Considering that people might still wonder on do fish need darkness to sleep, do not be surprised if they dozed off during the day or when there is poor lighting in the tank. It all boils down to how you set up the aquarium environment and how comfortable your fish feel in this new habitat.

Do fish sleep with room lights on? If yes, do they do it well? The simple answer is no. Fish do not doze off at ease if there is a lot of light in the aquarium. Irrespective of how slowly they move, do not leave your fish tank exposed to bright lights as it may cause your fish stress and frustration.

Dim lighting on during nighttime is just enough for these creatures to doze off peacefully. If you have a habit of watching them doze off, do not do it as it will disturb their sleep.

Most species of fish sleep at night for 5 to 10 hours long (generally). It is observed that they do this periodical pattern even during the day if there is good light in the aquarium. Some do only during the night while others do both. 

Can Fish Sleep With Blue Light On?

The different wavelengths of light do not disturb the dozing-off process of fish. However, do not leave your aquarium under blue light as it can make them look sickly and interfere with their appetite as well as the dozing-off process.

Blue light is used in some tanks to keep the tank illuminated while the occupants sleep.

As mentioned above, fish do not need darkness to sleep but do prefer either light or dark to sleep in.

Fish should be able to choose whether they want a lighted or darkened area of their tank for sleeping.

Can Fish Sleep With Room Lights On?

No, do not leave the tank in a lit area while dozing off to sleep. In nature, their habitats do not have any light when they are sleeping. Fish do not need darkness to sleep but do prefer either light or dark to sleep in.

Fish should be able to choose whether they want to doze off in light or darkness. Leaving the tank in a lit area can disturb their sleep, as well as stir them up from dozing off.

Do not place the aquarium near windows where sunlight gets through throughout the day. The sunlight coming through will change the temperature of your fish tank very quickly, causing them stress which could lead to health problems.

If dozing off in darkness is what your fish prefers, do not leave any lights on in the room that is housing your fish tank. However, do not place the tank near a window where moonlight gets through at night because this light can severely disturb their sleep as well.

Do Fish Prefer Light or Dark in the Aquarium?

Fish do not require a certain amount of darkness to fall asleep in but do prefer either light or dark to do so. 

Fish do not sleep the same way humans do and do not wake up at certain intervals to check the time or go to bed. 

Because fish do not require darkness, it is safe to keep room lights on while sleeping if others are trying to rest in your room. There will be no effect on fish behavior even with low lighting conditions.

What Happens If You Leave a Fish Tank In The Dark?

There is nothing to happen to a fish tank when we leave them in the dark. Fish do not need darkness to sleep. In fact, some fish do not even sleep at all!

Fish tanks do not need darkness to fall asleep. Some people say that leaving a room light on can harm the fish, but this is simply false information. Any bright light from a window or a lamp does not cause any harm to the fish tank.

Fish do not sleep in the dark, but they do need to rest. Fish do their best night swimming when it is dark outside. There are no other negative effects of keeping your fish tank in complete darkness than you might want to leave them in the light at times for your own comfort during viewing sessions. Do not confuse “night swimming” with sleep.

This is a common myth that has been circulating through the internet and it needs to be laid to rest. You do not need to keep your fish tank in complete darkness, you do not need any kind of light source for them to do well while swimming at night, and they do not “sleep” while they do their best night swimming.


It’s true that fish sleep, but they don’t need darkness to do it. Fish are capable of sleeping in many different conditions because their eyes are not sensitive to light like humans are. Sleep is critical for survival and well-being, even though most fish only get about 5 minutes per 4 hours spent awake! 

Have you ever seen your pet fish asleep? Share with us your experience in the comment section below.

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