Do Fish Lose Colour When They Sleep?


Most animals need to sleep or rest period so that they can get back their body process formation and fishes are no exception. You can almost tell when animals sleep as their eyes could be shut and they won’t respond to stimuli.  Even though fishes don’t sleep in the most convenient way, they do sleep too.

Several questions have arisen over time as to whether fishes sleep. Some people have even said they noticed changes in their fish’s colour when they sleep. In this article, therefore, we will be considering whether fishes lose colour when they sleep.

So, let’s get started.

Do Fish Lose Colour When They Sleep?

So, fish can lose colour when they sleep at night. Usually, when fishes sleep at night, they seem to take on resting colours. This means that as they sleep, their colour pigment seems to be relaxed and their colours become a bit dull.

Here is what happens. Fishes have pigment-producing cells that are responsible for their bright colours and this happens when the pigment closes together. However, when the fish is resting or sleeping, there will be no need to produce colours or use up energy. In this case, the pigment cells spread apart and this will make the colours of the fish a bit dull.

This is why when you turn on your fish tank light early in the morning, the fish could get startled for a few minutes. So, it is best to always turn on the room light for a while first before going for the tank light. This will help the fish gradually adapt.

How Do Fish Sleep?

Most times, when fish sleep, they remain still and their breathing slows down. In fact, you could even pick some with your hand as they sleep. The sleep habits could vary across different species of fish. Some fishes even sleep generally at night while others are active through the night.

Fish need oxygen to survive and their movement helps them get the oxygen as water passes through their gills. Some might receive this oxygen when they are in an almost stationary position as they face a current, move a fin or even stay afloat. This also happens as water passes around them.

Large fish like sharks have to make large movements for them to take in oxygen. This means that this fish could be sleeping and yet be moving. With such kind of sleep mode, one part of the brain of fish could be sleeping while the other half stays active. This is why the fish can keep moving even though it will be slower than when they are awake.

Some fish could go into a state of hibernation as they sleep even though this is associated with dry climates. However, some fishes could hibernate when they are deprived of food and water. Some fishes could even change their sleep pattern based on their access to food. This means that whenever they have food, they sleep less. When they have less food, they tend to sleep more.

Colour changes are also something notable about sleeping in fish. As they tend to go into their rest mode at night, they become particularly dull in colour. Although some fishes still maintain the same colour whether at night or during the day.

Where Do Fish Sleep?

Where fish sleep differs with varying species. While some fishes can decide to lay at the bottom, some could go ahead and bury themselves in the sand and some could even drift motionlessly along the surface of the water.

Some fishes could even decide to nestle into plants, driftwood, or other objects that they can find around. Some aquarium keepers might panic when they see their fish just lying at the bottom of the tank or being stuck in an ornament or a log. However, most often than not, aquarium species usually do this when they are sleeping.

When Do Fish Sleep?

Some scientists believe that fish could have regular sleeping schedules just as humans do. However, there have been slight differences that have been noticed in the sleeping pattern of fishes over time. While some fish could be diurnal which means that they move about during the day and take time to rest at night, some fish have shown different tendencies.

Some fishes are what we can call nocturnal which means that they could go into a cave during the day, take cover with a plant and spend hours sleeping. Then, at night, they start prowling. This could be a problem for you as an aquarium keeper particularly if you keep fish with different sleeping patterns together.

A good example will be putting small tetras such as Neons and large-mouthed catfish such as pictus cats together. While Neons will want to take cover and huddle around the tank at night, the catfish could be going around looking for a meal and disturb the neon.

Some fish don’t even sleep when they start caring for their young ones. They have even been major observations in Tilapia that they don’t start sleeping until they are five or six months old. Some fish don’t sleep when they are migrating.

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How Can You Tell If Your Fish Is Sleeping?

dead fish

Asides from the fact that your fish could lose color, there could be other signs for you to know that your fish is sleeping. This can even be an indication as to whether the colouration change is any cause for alarm. So, some of those signs include:

  • Your fish might have not moved for a couple of minutes.
  • You might notice them just floating along with a spot or they might have gone to the bottom of the tank or taken cover with a coral.
  • They take a longer time to respond to stimuli. You could try this out with their light or drop food in their tank.
  • They rest around that same time daily.

If you have noticed your fish being less active and colour changes start appearing, you can look out for any of these signs to know if they are asleep. If they are asleep, then there is no need to panic. Their bright colors will return to place when they are awake.

How Do I Make Sure My Fish Gets Enough Rest?

The best way to do this is to work with the aquarium light. What you have to do is to put your aquarium light on a timer as this will help you give your fish a practical night and day schedule. You can also ensure that there is enough cover for your fish to move into when they want to take their rest. This will aid their sleeping well.

If your aquarium is in a room that is lighted up, putting off the lights and drawing down the curtains will help your fish sleep well.


Fish could sometimes change color whenever they want to sleep. Their colour-producing pigment tends to ease off as the fish goes to sleep and this can cause a fade in their colour. However, this is no cause for concern as it is just normal.

We have been able to show you when a fish sleeps, where it sleeps and its sleep pattern, so if you notice a colour change with any of our pointers, your fish is probably just sleeping. You could therefore leave them to rest well.

Written by Justin Michaels

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