Do my fish in the fish tank really sleep?


If you’ve ever looked at your aquarium and wondered if fish sleep, you are not alone. Along with other questions like, “Can dog be allergic to other dogs?” or “I wonder if birds think in chirps or words?” this topic is one that begs to get answered someday.

Do my fish in the fish tank really sleep? Fish not only sleep at night, but they do so for long periods of time. Some fish show signs of sleep deprivation and insomnia, and will catch up on their sleep as a human would. Fish sleep is different from human sleep in that fish never reach any kind of dream state or REM sleep.

But let’s break it down a little bit.

As we all agree. Sleep is a necessity for all living creatures. Plants, insects, birds, elephants and yes, fish as well, sleep. Sleep in insects is much different from sleep as humans understand it, and fish sleep is different still. While fish in the fish tank may not be dreaming of crazy adventures on the high sea, they do need to rest and recharge just like any other living thing.

Deep Sleep can be a Dangerous Fish Activity

Since fish must always be on the lookout for predators, they tend to reduce their activity in a “suspended animation” rather than pull the covers up to their fishy chins and snore.  Now, the new question arises: do fish have chins and can they snore? But these are topics for another day.

Fish will find places to hide away from hungry eyes. They can wedge themselves under a rock in the wild, or in the castle, you put in their aquarium if domesticated. Some may burrow down into the substrate or sand, or hide under leaves of plants; still, others may just float in place.

Some fish, like the Parrotfish, will excrete mucus to surround themselves as they rest.

During this time of rest and recuperation, a fish’s metabolic rate will decrease and he will appear to be almost “daydreaming.”  They seem to be on autopilot, with their only motion being the slow flicking of a tail or fin to maintain their balance.

With a few deeply slumbering exceptions, most fish will waken when disturbed or when you turn on their lights.   

In the wild, some sharks such as the requiem and bluehead shark sleep so deeply that researchers were able to lift them to the surface without waking them; such a deep sleep proves that it’s good to be the king in the sea.  

Some species of sharks and fish need to remain in motion while sleeping because they need to keep water moving through their gills to breathe; others have an adaptation called spiracles that force water past the gills and allow the fish to stop swimming for a good night’s sleep.

Many fish that swim in schools will sleep-swim within the group to keep themselves surrounded and safer from predators.

While humans can sleepwalk at night, but it is unknown if these fish sleep-swim to the refrigerator in the middle of the night to eat ice cream.

The Nature of Fish Sleep – How do Aquarium Fish Sleep?

Because fish don’t have eyelids, they sleep with their eyes open.  A YouTuber posted this video of her aquarium full of sleeping goldfish, showing the following classic signs of fishy slumber:

Slow movements of the fins while the fish stays in place:

Fish will keep themselves upright, balanced and in place with slow movements of their fins. These motions will not be giving them any focused directional movement. You will probably notice that your fish has a droopy tail, as well.

Decreased activity of the mouth:

During sleep periods, fish will decrease all activity including the movements of their mouth.

Lack of activity at a similar time daily:

Fish develop sleeping patterns, just like humans. They will doze around the same time every day.

Lying on the bottom of the fish tank or floating in one place:

Sleeping fish will hide near rocks or plants, burrow into the sand or substrate, or just float in place while resting

A decrease in alertness:

If you drop a flake of food in the aquarium next to your sleeping fish, he won’t acknowledge the treat right away.

Fading of the color of the fish:

A sleeping fish may have a very subtle fading of his color as he slumbers. This will return to normal when he awakens.

Fish Sleep Is Not The Same As Human Sleep.

Sleep as humans understand it involves the neocortex and a very definite change in the brain pattern during slumber. Your finned fish friend is beautiful, but he lacks a neocortex.

It is reasonable for scientists to assume that fish do not experience the deep, dreaming state of REM sleep.

Sleep for fish is simply a period of slower metabolism, decreased energy, and rest. Believe it or not, fish need almost as much sleep as humans do. Most fish included aquarium fish, require between 9 and 12 hours of sleep a day.

In fact, Zebrafish is a common freshwater fish who will exhibit signs of insomnia if not permitted to sleep and will catch up on lost sleep as soon as they can. Scientists are currently studying Zebrafish, hoping that they can find an effective cure for insomnia in humans.

Fish Problems that may Resemble Sleep

Fish will generally sleep in an upright position. They may be pointed slightly upwards or resting on the bottom of your fish tank, but they do not sleep on their backs or on their sides.

Fish sleep on a side or on back.

If you have a fish in your freshwater aquarium that appears to be sleeping on his side or on his back, a serious ailment known as swim bladder disease is the culprit.

While most common in bettas and goldfish swim bladder disease can strike any freshwater aquarium fish. It is usually caused by the fish overeating, gulping too much air, a disease process, or being in water that is too cold for his metabolism to function properly.

In essence, swim bladder disease is severe constipation in a fish. If your fish is lying on his back or side or experiencing bizarre swimming patterns such as side swimming, back swimming, or the inability to rise to the surface of the tank without sinking back to the bottom, you can treat swim bladder disease by separating him in order to raise the temperature in his tank, change his water, and keep him from eating for a few days.

To rule out an infection as the cause of the disease, treat him with broad-spectrum antibiotic drops.

Fish is dead or just sleeping?

Some people have been known to confuse a sleeping fish with a dead fish. Make sure your fish is actually dead before sending him to his watery resting place. Last but not least, keep in mind these couple points:

Check your fish’s eyes:

If his eyes are sunken, he is probably either dead or very sick.

Try to net the fish:  

A sleeping fish will waken and begin to struggle as he is being netted. Some fish are very sound sleepers, so give him a moment or two to waken fully and realize his plight before scooping and flushing.

Check for intentional movements of the fish fins and tail:

A sleeping fish will still move his fins and tail to remain in one place.

Check fish for movement of the gills:

If the gills are moving, the fish is breathing. Motionless gills mean that your fish has passed on to that big aquarium in the sky. Some fish are air breathers, however so, in the case of bettas or other labyrinth fish, this is not a sign of death by itself.

A very sick fish can look like he is sleeping. If you have determined your fish is still alive but very sick, research symptoms to see if medicating or a water change may help.

If you choose to end his suffering, you can euthanize it with clove oil. Separate the fish into a breeding/separate tank and add about 400mg of clove oil to one liter of water.

The clove oil will cause the fish to lose oxygen, and he will pass away peacefully. This method is far more acceptable than flushing your finned friend fish in the toilet bowl.

Turn off the Lights:  To Let Your Fish Sleep

Fish need periods of both light and dark, just like any other living creature. If you keep the lights on in your freshwater aquarium for over 12 hours at a time, you will risk stressing the fish and disturbing their sleep patterns.

Be aware of algae

In addition, you may increase the algae in your fish tanks by leaving the light on round the clock.

Aquarium lights also have the potential to raise the temperature in your aquarium water to unacceptable levels for your fish.

If you have tropical fish, a cycle of twelve hours of light and twelve of dark most closely resembles their native tropical conditions.

Use Automatic Timer

Setting the aquarium light on a timer is a great way to ensure that you do not forget to turn the lights on or off at the appropriate times.

Diurnal or Nocturnal?

Most freshwater fish are diurnal, meaning they are active during the day and sleep at night. Other fish, like knife fish, catfish, loaches, and eels and snails are most active at night, or so-called nocturnal.

You may consider a blue light set up that may be left on overnight; these mimic moonlight and are not as disturbing to the sleep patterns of your diurnal freshwater fish while allowing you to watch the activities of your nocturnal fish and snails.

Both nocturnal and freshwater fish can be kept in the same aquarium. As long as they are provided with periods of light and darkness, they will thrive. Some freshwater plants, however, prefer longer periods of light.

Research both the plants and the fish that you want to keep together to be sure they can co-exist peacefully with lighting requirements. Make sure to provide nocturnal fish places to hide and sleep while their diurnal tank mates are awake and active.

Black light for your fish tank

Black lights are not recommended for normal tropical fish as there have been problems reported with their health and vision when exposed to this light source.

Some fish, however, are bred to be viewed with black lights as they have bright, neon colors set against vivid neon backgrounds.

If you have fish that require a black light for optimal viewing, make sure that you do not look at the light itself for too long, or you can experience problems with your vision.

When choosing aquarium lighting, pick a system that uses fluorescent bulbs or LED rather than any standard light bulbs. The light provided by a standard bulb will get hot, promoting algae growth and unhealthy temperature variations for your freshwater fish or plants in the fish tank.

Old school bulb/neon aquarium lights

These old-school lighting systems are also dangerous; if you splash water on a hot standard bulb, it will immediately shatter. Fluorescent bulbs have several varieties for the fish enthusiast, from color enhancing bulbs to full spectrum daylight mimicking bulbs.

There are even fluorescent bulbs that will encourage your plants to grow.

LED aquarium lights

LED lighting is beneficial to plants as well. This lighting option can come in a wide array of colors, from the blue moonlight setups to colors that will enhance the look of your fish or tank.

They stay cool and are inexpensive to run. These lights are made to be water-resistant, increasing the safety of you and your fish tank members.

The LED light is an easy way to avoid disaster after which you need to net shattered pieces of the bulb from your fish tank. LED lights for fish tank are always better option compare to regular bulbs neverthelss these days are even affordable, check price on Amazon in the link. 

Red light for your fish tank

Red lights have been used to light a tank at night to observe the fish. It has been reported that fish do not see the color red, so using red light will not affect their day and night habits. Keep in mind, red lights do, however, encourage algae growth in the fish tank.

So Fish Do Sleep Wrap-Up:

  • Fish not only sleep at night, but they do so for long periods of time.  
  • Some fish show signs of sleep deprivation and insomnia, and will catch up on their sleep as a human would.  
  • Fish sleep is different from human sleep in that fish never reach any kind of dream state or REM sleep.
  • Lacking eyelids, fish sleep with their eyes open, making it hard to tell if they are asleep or not.  
  • Fish can sleep in many ways; floating in place, buried in the sand or gravel, anchored under a plant, or hiding in decoration caves.
  • Fish do show some signs of being asleep like being unaware of their surroundings, slowed fin and tail movements, less frequent mouth movements, and became inactive around the same time every day or night.  

TIP: It is essential for the health of your fish to maintain periods of light and dark with aquarium lighting, simulating daytime and night time, and to be sure all fish have appropriate places to hide while sleeping

This should answer any question about fish sleeping. The question raised earlier about fish chins and snoring, however, will have to wait for another day, Cheers.

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