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Like other species, many fish require a goodnight of rest in order to be healthy. So if you see your fish sleeping upside down, should you leave them be?

Normally, fish sleep in an upright position throughout the night. Remaining upside down or on its side for an extended period of time is a sign the fish may have an illness such as Swim Bladder Disease. If the fish sleeps upside down, check it for other symptoms and get treatment when necessary. 

Seeing your fish upside down or on its side at any point of the day can be worrying, but it can easily be written off as just a quirky habit. Keep reading to learn more about how fish sleep and what to do if your fish is laying upside down.

Healthy Fish Sleep Rightside Up

Many do not realize fish even sleep at all. For the few that do acknowledge their fish’s fatigue, they are left wondering how their fish sleeps and what behaviors should be considered normal.

First thing first, fish do sleep. Just because your fish always has its eyes open does not mean that it is not getting some much-needed rest. In fact, fish have no choice but to sleep with their eyes open, they do not have any eyelids.

The only type of fish with an eyelid remotely similar to that of humans is sharks. Even then, they don’t work the same as ours.

Because fish have no eyelids, it makes having darkness that much more important. If your tank has lights be sure to turn them off overnight to give your fish a better night’s sleep.

As for what position your fish sleeps in, they should not sleep on their sides or upside down.

A healthy fish sleeps on its stomach in an upright position. They will often move their fins slightly to keep themselves in a stable position while they rest.

As well as sleeping upright, fish will typically rest at the bottom of their tank under any available foliage.

Your resting fish should also wake easily. Resting fish remain partially active in case a predator comes upon them.

If your fish is sleeping upside down or is hard to wake, they may have a serious illness resulting in a Swim Bladder Disease.

Treating Swim Bladder Disease


The most common symptom of Swim Bladder Disease in fish is lying sideways or upside down. If your fish is exhibiting this symptom they need immediate treatment.

Although Swim Bladder Disease is referred to as a “disease” it is actually a symptom of another illness. In order to treat the Swim Bladder Disease, it is important to know what could have been the cause.

The most frequent causes of Swim Bladder Disease are dirty water, inconsistent water temperatures, and improper feeding.

Learn more about why your fish may be swimming upside down here: Here’s why your Goldfish is Swimming Sideways.

Dirty Water

Fish were made for a life underwater. But the water they were made for is chemical-free out in nature.

Our drinking water contains chemicals such as chlorine to ensure its safe for us; however, these chemicals make the water unsafe for fish to live in. We add water conditioners and filters to combat these issues.

Although filters and conditioners help, it is still important to change your fish’s tank water every two to four weeks. If you wait any longer chemicals or bacteria make the fish sick resulting in Swim Bladder Disease or death.

Inconsistent Water Temperature

Aquarium fish are extremely sensitive to the environment around them. Not only does the water need to be clean, but it also needs to remain at a certain temperature too.

Any sudden changes in water temperature could shock the fish and strain the swim bladder.

Keep the tank at a consistent temperature in order to keep your fish happy and healthy.

Improper Feeding

In nature fish come across plants and bugs to eat quite frequently; however, in our aquariums, their diet is restricted to only what we feed them. Because of this, we need to make sure what we feed them is actually safe and healthy.

Foods that expand over time with water are not safe for fish. They can expand within their stomach leading to constipation and strain on the swim bladder.

Some flakey foods that sit on the surface can also be dangerous for our fish. Because they sit on the surface of the water the fish have to ingest air to eat them. This throws off how their swim bladder is regulated.

Another issue arising from feeding is overeating. Because fish are restricted to eating only when we feed them, they tend to eat as much as they can. Unfortunately, if we overfeed our fish it can lead to constipation, Swim Bladder Disease, and death.

If your fish has overeaten restrict their food until they have pooped.

Another option for helping constipated fish is to feed them small portions of frozen peas. The nutrients in the peas will soften the blockage and allow your fish to regulate digestion.

Treating your fish’s Swim Bladder Disease requires minimal effort but must be addressed immediately if they are going to survive.

Why Do Fish Sleep?

The reasoning behind sleep has been a mystery for a long. Today we understand that humans need sleep in order to recharge, heal, and fight off illnesses. But why do fish need sleep?

The answer is, that not all fish do.

Although tank fish have few currents to battle, their wild cousins are almost always in motion. For example, ocean fish are constantly in motion, and therefore sleep is not possible.

Another type of fish that does not require fish is those that are blind and/or live in caves. Cave-dwelling and blind fish do not encounter light or visual information and therefore remain awake at all times.

Scientists now believe fish use sleep as a time to process the visual information from the day (similar to human sleep). Each day your fish needs some time to sleep in order to process information; however, sleep deprivation will not affect your aquatic friends the same way it does us.


Hi, my name is Jordan. I've been in the fishkeeping hobby since my childhood. Welcome to my blog where I help fishkeepers enjoy the hobby by offering free guides, advice, & product reviews. Read more...