Are Your Fish Swimming in Circles? Let’s Check Out Why

Alison Page

Alison Page


fish swimming in circle

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One of the joys of keeping fish in aquariums is watching your fish enjoy the habitat you’ve created for them.

Different fish species gravitate toward different areas of the water column, and many have different swimming styles.

But why is your fish swimming in circles, and is that normal behavior?

Read this guide to learn the potential reasons why fish sometimes swim in circles, how to recognize problems, and what you can do to help your pet.

Why Is My Fish Swimming In Circles?

There are many reasons why your fish might be swimming in circles.

Your fishy friend could be stressed, suffering from whirling disease, displaying spawning behavior, or simply having a good time!

Here are the most common reasons for fish to behave in that way.

Just Having Fun!

If you have a dog, you’ll almost certainly have seen him chasing his tail. Well, some fish species behave in the same way!

So, if you notice your fish chasing each other and swimming in circles, there’s probably nothing to be concerned about.

However, always check that the water temperature is correct and the levels of ammonia and nitrite are zero. Nitrates should ideally be below 30 ppm.


Many fish swim in circles as a perfectly normal spawning behavior.

You might see your fish swimming around each other in circles before shimmying against each other to mate.

Some male fish swim in small circles to attract the attention of a female as part of a kind of courting dance.

Territorial Behavior

Lots of fish species, such as bettas and some species of cichlids, are highly territorial.

If your fish tank is in pristine condition and your fish are healthy, swimming around in circles can be a way for the fish to create a boundary or territory.

That can be the case if you recently moved your fish to a new tank or rearranged the decorations in your existing aquarium.

In that case, the mild stress of a change of scenery and the need to mark out a new territory can be enough to trigger your fish to swim in circles.

Ammonia Poisoning

Ammonia poisoning can be lethal to fish and can cause them to swim erratically or in circles.

When uneaten food, decaying plant matter, and fish waste are left to accumulate in your aquarium, they gradually decompose, releasing ammonia into the water.

Ammonia is sometimes called the “invisible killer” in fish tanks. One day your fish are fine, happy, and healthy, and the next, they’re dying.

Ammonia burns attack the fish’s exposed gill tissue, eventually impacting the central nervous system and the fish’s brain, and ultimately causing death.

What Causes Ammonia Poisoning?

The causes of ammonia poisoning include:

  • overcrowding
  • inadequate filtration
  • poor tank maintenance
  • poor water conditions
  • overfeeding
  • medication killing beneficial bacterial colonies that would otherwise process ammonia and nitrates
  • the filtration system not working properly, causing a low flow rate through the tank

So, how do you know that your fish are suffering from ammonia poisoning?

Ammonia Poisoning Symptoms

Here are the common signs and symptoms of ammonia poisoning in fish:

  • gasping desperately at the water’s surface, struggling to breathe
  • swimming rapidly in circles
  • clamped or tucked fins
  • red, purple, or bleeding gills
  • darkening in body color
  • rapid respiration
  • lethargy, often lying on the substrate
  • appetite loss

How To Treat Ammonia Poisoning

In a properly maintained tank with the correct water parameters, ammonia poisoning should not be a problem.

In fact, the levels of ammonia and nitrite in the tank should always be zero. Levels of nitrate should be 30 ppm or lower.

If you spot any of the aforementioned symptoms in your fish, test your aquarium water right away using an aquarium water testing kit. If ammonia levels in your tank are too high, take the following action:

  • Immediately stop feeding your fish. Your fish most likely won’t be eating anyway, and adding more food to the tank will only serve to increase the build-up of ammonia.
  • Remove ammonia from the tank by performing small, frequent water changes.
  • Use an air pump or water pump to aerate the aquarium.

Carrying out the above tasks will treat the problem of ammonia poisoning immediately. However, you must take action to ensure that the problem doesn’t recur in the future.

So, don’t overfeed your fish, avoid overcrowding the tank, keep the aquarium filter clean and functioning properly, and carry out weekly water changes to keep the tank water fresh and clean.

Whirling Disease

Whirling disease can cause infected fish to swim in circles, and is an infection in fish that’s caused by the Myxobolus cerebralis species of parasite.

Although it’s most common in salmonid fish, such as rainbow trout, whitefish, and cutthroat trout, Whirling disease also affects several species of aquarium fish, including goldfish, tetras, corydoras catfish, and discus.

The parasite gets inside the fish’s body, where it infects the creature’s brain and inner ear, causing neurological damage.

The water temperature, as well as the age and size of the fish, determine the susceptibility of individuals to this disease. However, juvenile fish are thought to be the most vulnerable to its effects.

What Causes Whirling Disease?

The Myxobolus cerebralis parasite can be present in freshwater oligochaete worms (tubifex) or in an infected fish.

So, be mindful of that if you buy your fish from breeders who use tubifex worms as a cheap protein source for their fish.

Whirling Disease Symptoms

Fish with Whirling disease display a range of symptoms, including:

  • Erratic tail-chasing behavior or whirling in a corkscrew-like pattern
  • Rapid breathing
  • Deformed head
  • Twisted spine
  • A black or dark-colored tail

The symptoms of Whirling disease typically appear after 35 to 80 days of catching the disease. Although the fish might survive, it will be unable to feed, swim, or escape aggressive fish and predators.

There’s no known treatment or cure for Whirling disease in fish. So, preventing your fish from being affected is the best way forward.

Avoid feeding your fish live foods, and stick to using frozen worms as a source of meaty protein for your fish.


fish swimming in circle

When a fish is stressed, its immune system is compromised, leaving the creature vulnerable to disease and a failure to thrive.

Swimming in circles, along with other odd behavior, can be a sign that your fish is stressed. You can take steps to remove stress from your fish’s environment once you’ve worked out the cause of their distress.

Poor Aquarium Conditions

As well as poor water conditions, as discussed earlier, overstocking your tank is a major cause of fish stress and illness in aquarium fish.

Overstocking causes oxygen depletion and water pollution and can lead to bullying and fighting at feeding times and for territory in the tank.

Remember to monitor the aquarium water temperature by fitting a reliable thermometer to your tank.

You should also regularly check the tank water parameters, including pH, ammonia, nitrite, and nitrate levels. If the levels are incorrect for the fish species you’re keeping or are prone to fluctuation; your fish will become acutely stressed.

Finally, you need to check that your aquarium equipment, including the heater, filter unit, and thermometer, is working correctly.

Unsuitable Tank Mates

If you have a community tank, it’s essential that all your fish get along. If you have a bully or a highly territorial fish in your collection, that’s bound to cause trouble and stress.

Fighting and injuries can even result if you have the wrong tank mates in your aquarium.

You can keep stress in a community tank to a minimum by providing your fish with plenty of hiding places where shy, smaller fish can take shelter if they feel the need.

Incorrect Diet

Poor quality or incorrect nutrition can be a major cause of stress in fish, so research your fish carefully to find out exactly what kind of food they need.

Most tropical fish can do well on a portion of well-balanced high-quality flake food, with some frozen meaty foods included in their diet to add variety.

Medication Reaction

If you need to treat your fish with medication, bear in mind that exposure to those chemicals can be highly stressful for your pets. That’s because chemicals and medicines can sometimes change the water’s chemistry.

In fact, medicines containing copper can kill some species of fish and invertebrates. So, it’s imperative that you double-check the likely effect of any medicines on your pets before you give them to your fish.

We recommend that you treat infected or sick fish in a separate quarantine tank rather than dosing your main display setup.

Swim Bladder Disease

Swim Bladder disorder is a common problem for many species of aquarium fish, especially Fancy goldfish and betta fish.

Swim Bladder disease is actually not a disease or infection, but rather a problem with the fish’s swim bladder.

The Swim Bladder is a gas-filled organ that regulates the fish’s buoyancy. Many things can cause swim bladder disorders, including physical deformities, bacterial diseases, and even environmental factors.

Causes of Swim Bladder Disorder

  • One main cause of swim bladder problems is overfeeding. Giving your fish too much food causes constipation and enlarges the fish’s gut and digestive tract so that the swim bladder becomes compressed. That leaves the fish with buoyancy problems.
  • If the tank has low levels of dissolved oxygen, the fish might gulp air at the water’s surface. That can also cause swim bladder problems.
  • If the water temperature in the tank is too low, the fish’s digestive processes will slow down. That causes food to back up into the digestive tract, ultimately resulting in swollen intestines, which puts pressure on the swim bladder.
  • Sometimes, bacterial infections can cause swim bladder problems.

Does My Fish Have Swim Bladder Disease?

Fish with swim bladder disorders struggle to remain on an even keel, often swimming on one side, with their head down, or completely upside down.

Often, the fish will float on the water’s surface or rest on the substrate, seemingly unable to swim to the surface.

A fish that can’t swim will struggle to feed. That means the fish will suffer from considerable stress and could even starve.

Your fish might even begin to display a bloated belly or curved spine if the problem is prolonged and severe.

What Can I Do?

So, what steps can you take to fix your fish’s swim bladder disorder?

Here are a few things you can try to help your fishy friends.

Fast Your Fish

You should stop feeding your fish immediately. Starve your fish for at least 24 hours so that the fish’s digestive system has a chance to clear any partially digested food.

Prepare a single, cooked frozen pea by removing its shell and feeding it to your fish.

Sometimes, that can be enough to get things moving through your fish’s digestive tract again and resolve the swim bladder problem.

Salt Bath

Make an Epsom salt bath by dissolving one teaspoon of Epsom salt per gallon of water in a small container. Pop the affected fish in the container for 10 to 15 minutes.

Give Anti-bacterial Medication

Sometimes, Swim Bladder disease can be caused by an infection or even a parasite. Try treating your fish with anti-bacterial or anti-parasite medication.


Keep your aquarium temperature between 75 and 80 degrees Fahrenheit. A slightly warmer water temperature can often help to encourage the fish’s digestive system to work more efficiently and cure the swim bladder problem.

Don’t Overfeed Your Fish!

As we explained earlier, overfeeding your fish can cause swim bladder problems. So, be sure to feed your fish the correct diet and in moderation.

It actually works well to fast your fish for one day per week. That gives the fish’s system a chance to process any food that’s remaining in its gut before you add more to the queue.

Most fish will graze on algae throughout the day, so you needn’t worry that your fish will starve or suffer from a day without its usual food.

How Long Can a Fish Survive With Swim Bladder Disorder?

Not every fish with swim bladder problems is going to die. The outcome really depends on what’s causing the condition in the first place.

Provided the swim bladder condition is not caused by a severe bacterial infection; usually, a change to the fish’s diet is all that’s required to put things back on track.


Here are the answers to a few of the most commonly asked questions about fish swimming in circles.

Q: Why Is Your Fish Spazzing Out (Shimmying?)

A: Fish suffering from shimmying typically rock from side to side. Sometimes, the fish might clamp its fins, yawn, headshake, or display labored or very heavy breathing.

Shimmying is a symptom rather than a disease and happens when the fish loses control of its nerves and muscles. Fish with shimmies can be suffering from stress, water chemistry issues, or even poisoning.

Sometimes, the fish might vibrate, shake, or twitch its body for short periods and could also have cloudy eyes, bloating, and display excessive slime production.

To confuse matters, some perfectly healthy fish species shimmy against each other for brief periods when spawning.

Q: Why Is Your Fish Swimming in Jerking Movements (Twitching?)

A: Twitching is a spontaneous muscular contraction of the fish’s body when the creature moves in a jerky, rapid spasm.

The movement is involuntary and affects the fish’s pectoral fins and mouths, as well as the body. If the fish also has reddened skin, swelling, labored breathing, and a loss of color, that’s usually indicative of an infection.

Sometimes, twitching can be caused by stress following environmental changes and even boredom if the tank lacks decorations, planting, and tank mates to stimulate the fish.

Forgetting to feed your fish can also trigger twitching! Poor water quality and incorrect water temperature can sometimes cause fish to twitch.

Finally, if the fish has an underlying health issue, such as a parasite attached to its body, that can cause the creature to twitch in an effort to shift the nuisance pest.

For example, fish that are suffering from Ich often flash or flick against rough objects in the tank as they try to dislodge the irritating parasites.

Q: Why Is My Fish Swimming Fast Back and Forth?

A: The most usual cause of a fish darting back and forth is significant stress.

The fish might swim frantically around the tank, apparently going nowhere. Affected fish often crash into decorations, clamp their fins, and flash or rub against the substrate or other solid objects in the tank.

However, if the fish develops a rash of white spots across its body, gills, and fins, the problem could be caused by White Spot Disease or Ich.

Ich is relatively easy to treat with an over-the-counter medication that you’ll get from your local fish store or pet shop.

Q: Why Is My Fish Swimming Upside Down?

A: The main reason for a fish to swim upside down is a swim bladder problem.

The swim bladder is the organ that enables the fish to remain upright and swim on an even keel. Problems with the swim bladder’s function can cause the fish to swim on one side or even upside down.

Swim bladder problems are quite common in Fancy goldfish and bettas. The condition is usually caused by:

  • Constipation, causing an excessive build-up of food to press against the swim bladder
  • Gulping air at the water’s surface when feeding
  • Eating an incorrect diet
  • Sudden fluctuations in temperature
  • Bacterial infection
  • Attack by parasites

Fancy goldfish can develop swim bladder problems as they mature simply because of excessive crossbreeding that’s been carried out by breeders trying to produce more and more unusual and extreme body shapes in their fish.

Q: Why Is My Fish Swimming Erratically After a Water Change?

A: Fish sometimes swim erratically following a water change, generally due to a condition called osmotic shock.

Osmotic shock occurs when the fish cannot regulate its uptake of ionic compounds, leading to the fish releasing or absorbing too much fluid.

That impaired osmoregulation can lead to a condition called dropsy, which causes erratic swimming patterns.

Final Thoughts

I hope you enjoyed our guide to why your fish might be swimming in circles. If you found the article helpful, please take a minute to share it!

There are a variety of reasons why your tropical fish might start swimming in rapid circles.

Your fish could be suffering from a bacterial disease or a common parasite infection, poor water quality in your fish tank could be to blame, or your fish might have Swim Bladder disease.

Perhaps a change in environment or the introduction of new fish to a community is to blame.

Once you’ve worked out the cause of your fish’s odd behavior, you can take steps to fix the problem as outlined above.

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