Fish Swimming in Circles: 10 Reasons

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Maybe you’ve noticed your fish swim in circular motions. Is it normal? Is this something you should worry about?

It is not uncommon for fish to cruise in circles. There could be many different causes of this odd behavior.

For example, males can behave this way when protecting their territory. Sometimes the reasons can be very serious.

Continue reading to discover the main reasons why fish swim in circles. Aside from the causes and symptoms, you will also find some effective remedies and tips on how to treat this issue.

Top 10 Reasons Why Aquarium Fish Swim in Circles

fish swimming in circles
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Erratic or strange swimming behavior is a frequent occurrence in aquarium fish. That’s not to say you should ignore it.

As a fishkeeper, you need to know why your fish is swimming in circles. If you identify the reason behind this uneasiness, you’ll be able to choose the most suitable remedy to stop it.

Circular swimming is a way of expressing feelings of discomfort in general. However, the causes might be various.

1. Swim Bladder Disorder

Fish have a swim bladder that is filled with gas and helps them maintain buoyancy. When the function of this essential body organ is out of order, it can lead to a condition called swim bladder disease.

This illness/disorder can cause fish to sink to the bottom or float upside down. Likewise, it may get them to swim in circles.

Swim bladder disorder is common in betta fish and goldfish. Besides them, it can affect other tropical aquarium fish, too.


Fish suffering from this problem show certain buoyancy signs that are easy to spot. Don’t be surprised if you notice fish lying at the bottom of your aquarium or floating at the surface.

While swimming, affected fish have difficulty maintaining their usual body position. They swim head down, upside down, or on the side.

In addition, you may notice some odd physical changes such as a bloated stomach and curved spine. It may also be a symptom of swim bladder disorder.


There might be different causes of swim bladder disease or disorder. This condition can be caused by many factors including poor water quality, bacterial infection, and injury.

Sometimes it is associated with physical abnormalities in fish as well as environmental or mechanical factors. Listed below are the most common causes:

  • Gulping too much air while grabbing food from the surface of the water.
  • Overfeeding – It can cause constipation in fish and enlarge their abdomen, which leads to compression of the swim bladder and affects buoyancy.
  • Catching various infections.
  • Low water temperature – It can make the intestines become larger, thereby putting strain on the fish’s swim bladder.


Prevention is better than cure. The best way to prevent this condition from occurring is by maintaining good water quality and ensuring that your fish are not suffering from any injuries.

Other treatment options include:

  • Placing affected fish in an appropriate salt solution, thus relieving the stress linked to swim bladder disorders.
  • Changing nutrition – Don’t feed fish for 3 or more days. After that time, offer microwaved or boiled peas without the shell in small amounts.
  • Using commercial antibiotics and remedies against parasites in case swim bladder disease is caused by infection.

2. Whirling Disease

Whirling disease is caused by Myxobolus cerebralis, a parasite that typically infects salmonids. However, it may also be found in other types of aquarium fish like tetras, goldfish, discus fish, and corydoras.

The susceptibility to this infection is dependent on different factors, including water temperature as well as the size and age of the fish. Adults turned out to be less vulnerable than young fish.

Once the parasite has entered the body, it causes infection in the brain and inner ear. This eventually results in neurological damage.

This condition causes the fish to swim in whirling patterns, which can lead to death sometimes. That’s why it is critical to identify symptoms on time.


As the name suggests, fish with this disease usually display whirling behavior. It can also manifest as tail chasing.

In addition to creating corkscrew-like patterns and rapid breathing, it is also characterized by convulsive movements.

Keep in mind that infected fish usually begin to exhibit symptoms 40-70 days after acquiring this illness. Here are the physical appearance changes that are the common symptoms of the whirling disease:

  • Darkened or black tail
  • Head deformities
  • Twisted spine

NOTE: Just because these symptoms occur doesn’t necessarily mean your fish suffer from the whirling disease. Furthermore, they don’t always appear in sick fish. Microscopic examination is the only sure way to determine the infection.


The whirling disease may not cause the death of your infected fish. Still, it can impact their ability to eat, breathe, and swim.

That is why it’s important to act fast after diagnosing the disease. Sadly, there’s still no remedy that can effectively treat whirling disease.

The best way to deal with this illness is to keep it under control in hatcheries. If managed carefully, hatchery environments can alleviate the consequences of the infection and prevent it from spreading.

3. Ammonia Poisoning

Ammonia poisoning in aquariums is a common problem that can be caused by many factors. This is usually a result of excessive fish waste and particles of rotting food.

Ammonia levels tend to spike abruptly over several days, especially if there are substantial changes in the chemistry of water.

If not controlled, high ammonia levels can impact gill tissue and other vital organs. For example, it can affect the central nervous system (CNS) and brain if left untreated. This leads to death.

That’s why it is regarded as an invisible killer in fish tanks. To prevent a fatality, it’s important to know the signs and how to treat this issue.

One of the symptoms is swimming in a circular motion. Read on for the symptoms, causes, treatment, and prevention of ammonia poisoning in aquariums.


Unfortunately, ammonia poisoning is tricky to recognize. In order to help you identify this problem in your tank, we will reveal the common clinical signs and symptoms of ammonia toxicity:


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  • Swimming in circles
  • Bleeding, purple, or red gills
  • Tucked or torn fins
  • Rapid breathing
  • Body color darkens
  • Loss of appetite
  • Lethargy


The following are the most common ammonia poisoning causes:

  • Poor water quality
  • Overfeeding
  • Overcrowding
  • Decaying organic matter
  • Decreased flow rate
  • Death of good bacteria in the tank

Prevention & Treatment

This common problem can be prevented or solved for good by following these simple steps:

  • Check the water condition of the tank regularly
  • Improve the water quality by performing frequent and small water changes
  • Install an ammonia or nitrite filter
  • Clean your filter on a regular basis
  • Use an air pump to aerate your tank if necessary
  • Stop overfeeding your fish
  • Avoid overcrowding your tank

4. Territorial Behavior

Aggressive territorial behavior is a natural part of the life cycle for many types of aquarium fish. Betta fish is a good example. It is most commonly observed in male fish during the breeding season.

A common sign of territorial behavior is swimming in circles. By swimming in a circle around a certain area, males (and rarely females) create a boundary in aquariums. This way they signal to others (especially males) that they are not welcome on their “property.”

While circular swimming is often a symptom of an illness or stress, you should consider other causes if the fish seems healthy and your tank features optimal conditions. One of the possible causes is territorial behavior.

It’s a response to the intrusion of an individual into the space of another. Fish will usually respond by displaying aggressive behavior when they feel their territory has been invaded.

5. Unhealthy Aquarium Conditions

Exposure to stress caused by overcrowding has a negative influence on fish behavior. One of the common stress-related behaviors is swimming in a circle.

An overstocked aquarium typically has bad water conditions, including pollution and oxygen depletion. So, avoid overstocking or overcrowding your tank!

You should also consider testing water parameters in your aquarium now and then. This will ensure that the conditions are not unhealthy.

Different factors can drive acute stress. Some of them include temperature fluctuations, low oxygen levels, and improper pH levels. Elevated nitrate and ammonia levels can also lead to stress in fish, which may cause them to swim in circles.

Additionally, you need to maintain your aquarium equipment from time to time. Make sure everything functions correctly to provide optimal conditions all the while.

6. Nutritional Stress

Stress can also be caused by improper diet. As a result of nutritional stress, fish may start to swim in circular motions.

Proper nutrition is essential for good health. Just like humans, different types of fish have different nutritional needs. That said, you need to know the nutritional requirements of the species you keep in your tank.

Many fish can survive in tanks on minimal nutrition. All you need to do is give them stale flake foods once or twice a day. Even so, you shouldn’t overlook the importance of their diet.

Make sure their diet is balanced to avoid health problems caused by nutritional stress. Poor nutrition can negatively affect the immune system of fish, which gives rise to different health issues.

7. Aggressive Tank Mates

Aggression in fish is not always associated with territorial behavior. It is often a result of wrong pairing.

That’s why those stocking community aquariums should choose compatible species. Otherwise, tank mates may hurt each other. In addition to injuries and infections, aggression can cause death.

Ample hiding space is a good way to lessen harassment in your tank. This is particularly helpful for smaller fish, as it allows them to hide from belligerent tank mates.

If you have unfriendly males in your tank, you should also consider shifting aggressive fish to a new aquarium. It’s not always a smart idea, though.

When changing a tank, fish may erratically swim in circles for hours. When will it stop? Well, once it becomes accustomed to new territory and adapts to a new environment.

8. Introducing Chemicals and Medications

Many fishkeepers add medication to their tanks to treat ailments while improving water conditions at the same time. However, many people don’t know that it’s often stressful for their fishy friends.

Exposure to chemicals can make fish stressed, causing them to swim in circles. That’s because some chemical substances can dramatically change the chemistry in aquariums. Thus, they can affect essential parameters that are important for favorable conditions.

Therefore, be careful when adding medication or chemicals to your tank. Try to find out more about them before application.

If you want to put an unknown medication, do not add it to the main tank. We recommend treating affected fish or diseases in separate containers, just in case.

9. Mating

Swimming in a circle is one of the mating signs in fish. That’s how they display such behavior sometimes.

This mating behavior is often confused with an illness. So, you are advised to consider other signs of mating, too.

Each type of fish displays distinctive signs. Be aware of them.

How do you treat this issue? In most cases, it will stop by itself once the breeding season is over. If it doesn’t stop, your best bet is to separate them.

10. Swimming in Circles for Fun

As playful aquarium pets, fish like to cruise around in circular motions occasionally. They actually chase their tails.

Therefore, it shouldn’t catch you by surprise when you see your fishy pets moving around circularly. If they are in good health, this behavior is likely associated with playfulness.

Don’t be concerned. They just have some fun!


Final Thoughts

Fish may swim in circles due to whirling disease, ammonia poisoning, or swim bladder disease. On other occasions, they do it because of exposure to chemicals or nutritional stress.

However, the reasons are not always serious. If your fish doesn’t have any health problems and the aquarium conditions are flawless, it might do it just for fun.

Nevertheless, you need to try figuring out the reason for this odd behavior. Hopefully, the information provided here will help you find out why your fish swim in a circle and pick the most effective treatment.

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