Do Aquarium Fish Sleep at Night?

As aquarium owners, we often wonder if our aquatic pets sleep like we do. It’s a common question, while fish don’t sleep like humans, they do have periods of rest that can be compared to sleep. In this post, we’re going to examine aquarium fish sleeping habits as well as the question, “Do aquarium fish sleep at night?”

Aquarium fish are fascinating creatures, and watching them swim in their aquatic world can be quite relaxing. As aquarium owners, we always try to recreate their natural habitat to provide a comfortable and stress-free environment. However, when it comes to their sleeping habits, many aquarium owners are unsure of what to expect.

What is Sleep?

Before diving into fish’s sleeping patterns, let’s first define what sleep is. Sleep is a state of rest characterized by reduced consciousness, decreased muscle activity, and slowed metabolism.

Sleep in humans is separated into two stages: non-REM (Rapid Eye Movement) sleep and REM sleep. During non-REM sleep, our bodies repair and regenerate tissues, while REM sleep is associated with dreaming.

Do Fish Sleep?

Fish don’t have eyelids, so they don’t close their eyes during sleep like humans. However, they do have periods of rest that can be compared to sleep. Aquarium fish sleep in short periods throughout the day, and unlike humans, they don’t experience deep sleep.

How Do Fish Rest?

Fish rest by reducing their activity levels and metabolism. They may stay still or hover in one place, and their breathing and heart rate may slow down. Some fish even rest on the bottom of the tank or hide in a cave or crevice.

Circadian Rhythm in Fish

Fish, like humans, have a circadian rhythm, a 24-hour cycle that governs sleep and other physiological activities.

In the wild, fish are exposed to natural light and dark cycles, which helps regulate their circadian rhythm. In captivity, artificial lighting can disrupt their sleep patterns and circadian rhythm.

Environmental Factors Affecting Fish Sleep

Several environmental factors can affect the sleeping patterns of aquarium fish. Water quality, temperature, and the presence of predators or tank mates can all impact their rest.

For example, if the water quality is poor or the temperature is too high or too low, it might stress the fish and disrupt their sleeping cycles.

Common Sleeping Habits of Aquarium Fish

Different species of fish have different sleeping habits. Some fish, like goldfish, tend to sleep more during the day and are active at night.

Other fish, like tetras, tend to rest for short periods throughout the day. Betta fish have been observed building a bubble nest and resting underneath it.

Can You Wake Up Sleeping Fish?

It’s not recommended to wake up sleeping fish. Fish need rest to stay healthy, and waking them up can stress and affect their sleeping patterns. If you need to check on your fish, it’s best to do so during their active hours.

Signs of a Healthy Fish

Healthy fish are active, alert, and have a good appetite. They should swim smoothly and have clear, bright eyes. If you notice any changes in their behavior or appearance, it could be a sign of stress or illness. Common signs of stress include lethargy, loss of appetite, and erratic swimming.

Sleep Deprivation in Fish

Fish, like humans, can experience sleep deprivation. Sleep deprivation can impair their immune system, alter their behavior, and make them more vulnerable to disease. Sleep deprivation might potentially result in death in extreme circumstances.

How to Promote Healthy Sleeping Habits in Aquarium Fish

To promote healthy sleeping habits in your aquarium fish, it’s important to create a comfortable and stress-free environment. Here are a few tips:

  • Provide a suitable hiding place for your fish to rest in
  • Maintain good water quality and temperature
  • Use a timer to regulate the lighting in the aquarium
  • Avoid sudden changes in the environment
  • Avoid overcrowding the tank
  • Feed your fish a balanced diet


In conclusion, while aquarium fish don’t sleep like humans, they do have periods of rest that can be compared to sleep. Different fish species have different sleeping habits, and environmental factors can affect their sleep patterns. As aquarium owners, it’s important to create a comfortable and stress-free environment to promote healthy sleeping habits in your fish.


Do fish need complete darkness to sleep?

No, fish don’t need complete darkness to sleep, but they do need a regular light and dark cycle.

Can fish die from lack of sleep?

Yes, lack of sleep can weaken the immune system and increase susceptibility to disease, potentially leading to death.

Can fish sleep while swimming?

Fish don’t sleep while swimming, but they may rest by staying still or hovering in one place.

How long do fish sleep?

Different fish species have different sleeping habits, but most fish rest for short periods throughout the day.

Can you overfeed fish?

Yes, overfeeding fish can lead to health problems, including obesity and poor water quality.

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