Freshwater Fish

Do goldfish sleep? How to know and for how long

Aquarists don’t often talk about whether their goldfish are getting enough rest, but this leads to an interesting question: do goldfish sleep? After all, they don’t have eyelids. How do fish sleep without closing their eyes? I’ll answer these perplexing questions and more as I introduce you to the mysteries of goldfish sleep cycles!

Sleeping Habits of Goldfish

Let’s tackle the main question first: Yes, Goldfish and other aquatic animals sleep. They don’t do this in the same way that humans or other mammals do and it may not always be obvious when they are asleep. After all, your goldfish doesn’t put on pajamas and lay down on a bed of Java Moss when you turn off the light.

Why do Goldfish need to sleep?

Just like humans and other animals, goldfish need regular periods of calm and quiet for their bodies and brains to rest. Sleep restores your energy and helps your immune system work properly to prevent illness and disease.

When your goldfish don’t get enough sleep, their metabolism can slow down and they lose their normally ravenous appetite. Their immune system begins to have problems and your goldfish may develop bacterial or fungal infections. Making sure your goldfish gets enough rest is important to maintaining a healthy fish tank!

How do goldfish rest?

A «sleeping» goldfish is not really asleep. Instead of going through stages of light and deep sleep cycles and losing consciousness like a mammal, goldfish rest while remaining peripherally aware of their surroundings. They take several short naps (with their eyes open) during a rest period instead of sleeping for a long time!

A sleeping goldfish can:

  • Float or float almost motionless in the tank, moving just enough to remain upright and stable in the water
  • Hover near bottom of tank or near decorations and plants, with head hanging slightly lower than tail.
  • They fade or lose color while they sleep and regain it when they wake up and become more active
  • Be less alert than when awake and slower to respond to normal stimuli, but may be startled by sudden or unexpected sounds or movements (such as a predator approaching them)

Do goldfish dream?

If you scan the brain of a goldfish during these rest cycles, you’ll see that it doesn’t go through the sleep stages. we are used to. Their brain waves do not change when they are resting and never enter the REM (rapid eye movement) stage where humans actively dream. As far as we know, goldfish do not dream when they sleep.

Do goldfish sleep upside down?

While goldfish can move about while napping, they remain mostly upright. While it is not unusual for them to sleep with their heads lower than their tails, or even to sleep on the bottom of the tank, it is not normal for a goldfish to turn upside down or on its side when sleeping. Those are signs of a sick fish, not a sleeping fish.

When do goldfish go to sleep?

Do goldfish nap at night or during the day? A bit of both, actually. Goldfish are not specifically diurnal or active during the day, but they are much better adapted for daytime hunting and exploration than for nocturnal activities. So it’s natural for your pet to sleep more when the lights are off than when they’re on.

Goldfish see almost the same spectrum of light as humans, but they can also see infrared and ultraviolet waves. This means that they can see better at dawn and dusk, when the light entering the water is highly polarized. But they really don’t see any better in the dark than we do. So wild fish are usually more active during the day than at night.

How long do they sleep?

Since goldfish don’t sleep like us, but rather rest during periods of low activity, it’s difficult to calculate exactly how long they spend asleep or awake. From my observations, I would estimate that the average goldfish sleeps 8-12 hours a day in short cycles of 10-30 minutes, with variations between fish and tanks.

It can also disrupt your fish’s sleep cycles. If your aquarium lights are on a regular 12-hour on/off cycle, they’ll learn to sleep when they’re off and be more active when you’re awake (and feed them)! A very bright or very noisy room will probably prevent them from sleeping as well, even if your light is off at night.

Differences Between Sleeping and Sick Goldfish

You should be able to easily tell the difference between a sick goldfish and a sleeping fish once you become familiar with your community members. Your goldfish will develop their own unique personalities and habits, and you will see changes when they get sick that stand out from their normal behavior.

Healthy goldfish respond to your approach to their tank, even if they are napping, and swim normally when awake. They also actively forage, eating heartily and usually displaying their most vivid colors while doing so. On the other hand, stressed or sick goldfish display alternate appearances and behaviors. Click here to find out more about your goldfish.

  • If your fish suddenly or gradually loses the ability to swim straight, swim in circles, float upside down, or cannot swim at all, they are sick and not sleeping.
    • Sleek Goldfish are especially prone to swim bladder problems that make it difficult for them to stand upright or swim in their tank.
  • Goldfish that lose their appetite and/or look paler than normal while awake may be sick or stressed for some reason

Reasons Your Goldfish May Sleep More Than Usual

Occasionally, you may notice that your goldfish seem to be sleeping more than usual or displaying other changes in behavior, such as constant yawning or suddenly acting aggressive towards their tankmates. These can be signs of stress and can lead to illness if not corrected in time. Some common reasons for goldfish lethargy include:

Water temperature fluctuations

Depending on the breed(s) of goldfish you have, the ideal water temperature can be very wide or quite narrow. Elegant goldfish are usually more sensitive to specific water temperatures, but no goldfish likes it when the temperature changes rapidly. Even a change of 5 degrees in a few hours could cause stress.

If you keep your goldfish in water that is too warm or cold for them, it is likely to make them lethargic and suppress their appetite, eventually leading to illness. Constant sleep lowers your metabolism and immune system and makes it more likely that you will get an opportunistic infection.

Tight tank conditions

Another thing that stresses a goldfish is not having enough room to swim. An undersized tank or one filled with other fish, plants, or decorations can lead to accidental injuries and negative behaviors such as biting and fighting over food. They usually become lethargic and eventually get sick in crowded tanks.

Toxic levels of ammonia

It is normal to see your goldfish yawning as this cleanses the gills. But they shouldn’t constantly yawn or gasp for air at the surface of the tank. These are signs of low oxygen levels and could indicate a toxic ammonia spike in your tank.

Goldfish are well known for their voracious appetites, and a side effect of their never-ending search for food is that they produce a large amount of biological waste. If you skip a few water changes, ammonia levels in your goldfish tank can quickly reach lethal levels. Sleepy or yawning goldfish can be a sign of high ammonia content in your tank.


Although goldfish cannot close their eyes, they do sleep at night and take naps during the day. It’s normal for them to sleep about 8-12 hours out of 24 in short bursts, and most fish learn to sleep when you don’t interact with them. Your goldfish needs plenty of rest to stay healthy and can get sick if they are deprived of sleep.

Excessive lethargy and constant yawning are not normal in goldfish and usually indicate problems with the temperature, environment, or quality of the water in your tank. I’d love to hear about your goldfish’s sleeping habits or answer more questions about the science of sleeping fish, so please comment below or send a note via social media.

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