Why Your Aquarium Fish is Swimming Erratically (In Circles)

By Eddie Waithaka @aquariawise

Why Your Aquarium Fish is Swimming Erratically (In Circles)

Updated, 24, August, 2022.

I have had this question and other ones alike, and the answer thrown around most times is I don’t know. Even so, some suggestions seem to have some bearing, particularly those bordering on the fish is acting this way because of a recent water change, general stress, poor water quality and so forth.

However, the answers are at best speculative because erratic swimming behavior in aquarium fish, can be premised on varying abnormal movements ranging from darting motion, corkscrew swimming manner, fish swimming in circles, fish swimming up and down and sometimes floating to the top, sinking to the bottom or swimming sideways or upside down.

That said, the most common reasons for aquarium fish swimming erratically, depending on what you consider erratic, is either stress (glass surfing), ammonia poisoning and poor water quality (in circles and darting motion), and swim bladder disease (floating to the top, swimming sideways or sinking to the bottom).

On lesser occasions, your fish may swim in a corkscrew manner, which is a sign of whirling disease caused by Myxozean parasite.

Read on for better insight.

Why Your Fish is Swimming in Circles

See video in r/aquarium, subreddit

When you have a single fish swimming in circles, frantically or in a darting motions, the most probably cause is the water quality, particualarly ammonia (in your water) and not the mating dance.

If you have two fish swimming in circles in your fish tank, it most likely a mating dance. This happens between a male and female fish. Your fish will also swim in circles from stress caused by poor water quality or chemistry (ammonia poisoning, pH fluctuations, off-temperatures), especially after water changes.

A mating dance will be occampanied by brief shows of aggression and other odd behavior like ‘kissing’, more so with fish like cichlids and gouramis, while poor water quality often comes with fish swiming in frantic, darting or jerking motions around the tank.

That said…

Swimming in circle is natural behavior in some fish, like betta, used to establish dominance in a the tank. Kuhli and weather loaches naturall like to swim in circles, especially when the weather is about to change or when a strom is coming.

Schooling fish swim in circles for security reasons. They use their strenght in numbers to discourage enemies, and in some cases to feed or even spawn.

Why Your Betta Fish is Swimming in Circles

Betta fish swimming in circles is a natural behavior used to display territorialism or a attract mate. Siamese fighting fish show this behavior around other bettas and colored, long-fin, similarly-sized fish.

Even so…

Betta fish may swim in circles for other reasons. Here are a few possibilities:

— Swim bladder disorder can affect a betta fish, causing it to swim in circles or float upside down. This condition is usually caused by constipation or bacterial infections, which affect the fish’s ability to control its buoyancy.

— Bettas are sensitive to changes in their environment and can become stressed by factors such as poor water quality, sudden changes in temperature, or overcrowding. Stress can cause a betta to swim in circles or display other odd behaviors.

— Betta fish are intelligent and require constant stimulation to keep them from getting bored. Your fish may become more aggressive and swim in circles or up and down the fish tank if it’s bored, especially if something interesting is going on outside his aquarium.

Why Your Fish Might Be Swimming Erratically

As I mentioned above, there are several reasons why your aquarium fish might be swimming in an abnormal manner. Some situations are not very serious, but others you should be concerned about.

Below are the five main reasons aquarium fish would swim erratically.

Ammonia Poisoning (+Poor Water Quality)

If your fish is swimming frantically, particularly in a jerky, darting motion, this means it may be suffering from ammonia poisoning or reacting to poor water conditions in the tank.

However, the fish could be playing or exercising, so look for other signs such as the fish looking generally unhealthy, swimming in rapid circles, tucked fins, and in severe cases, ammonia burns and affected areas turning black.

Rapid breathing, lethargy, and fish gasping at the surface are also signs of ammonia poisoning in aquarium fish.

Ammonia is a by-product of rotting food and fish waste in the water column, which can potentially poison and even kill your fish. Therefore, test you water ph, ammonia and nitrites immediately you notice any of the said signs.

It is recommended that both ammonia and nitrites levels in aquariums remain at 0ppm because they are toxic to fish. Nitrates are not as toxic in high concentrations.

The recommended nitrates level in freshwater tanks is 20ppm.

To treat ammonia poisoning in your fish, you want to stop feeding for a while, which makes them produce less ammonia. Also, aerate your tank with either an air pump or water pump since ammonia make it hard for fish to get oxygen from water.

Then perform a water change, test the tank for ammonia and nitrite, and repeat the process until the levels are at or near 0ppm.

In the long term, try not to overfeed your fish and ensure you don’t overstock your tank. Each inch of fish you have should have at least a gallon of water space.

Glass Surfing

See video in r/aquarium, subreddit

Aquarium fish exhibit many swimming behaviors as clues to how they are feeling, and glass surfing or pacing is one of them; this is when fish constantly swim up and down the side of the aquarium glass.

Mostly, fish do this when they are stressed or unhappy with their environment. However, it could also be they are just curious and like playing detective, which is common with bettas.

Thats said, if you notice your fish pacing, it is important to investigate what might be causing this behavior. Most likely, there is something you can change in their environment that will help them to calm down.

In most cases, the issue comes down to poor stocking, tank size, and tankmate choices. Even so, the wrong water ph or temperature for the fish you are keeping might be the cause.

A thing to note is that stress is a major cause of aquarium fish untimely deaths, so watch out for signs of stress such as this one and take action to reduce it.

As mentioned before, the main causes of stress in tropical fish is poor water chemistry, overstocking, wrong pairing, loneliness, and overfeeding or starving your fish.

Swim Bladder Disease

Swim bladder disorder in aquarium fish refers to several issues affecting the swim bladder rather than a single disease. It is common in goldfish and bettas, though it can strike other tropical fish species.

The disorder is manifested when the swim bladder does not function normally due to disease, physical disorder, or environmental factors like water temperature.

Overfeeding, which leads to constipation, and fish gulping air when they grab food from the surface of the water can also cause this disorder.

Fish with swim bladder disease show several signs that relate to buoyancy, including swimming difficulties. Normally, an affected fish will either sink to the bottom or float at the top of the tank. Also, it will struggle to maintain a normal body position and will instead swim either on its side, upside down, or even head down. The spine will look curved, and the belly area will seem full or bloated.

To keep your fish from getting swim bladder disease, keep the water in your tank clean at all times, and the temperature between 75 and 80 degrees Fahrenheit.

Also, cook dried foods and thaw frozen foods before feeding them to your fish, and make sure you only give them the appropriate amount.

Fish Swimming Erratically After Water Change

If your fish is swimming erratically after a water change, it means there is an abrupt change in your water parameters. The new water might have spiked (or lowered) the pH or temperature in your fish tank or interfered with the Nitrogen cycles, causing a rise in ammonia or nitrite levels.

Note that, while a slight change in the temperature or pH to what your fish is used too may not be fatal, an abrupt change will send your fish into shock and may even kill it.

In the case of an increase in ammonia and nitrites in the fish tank, your fish will also have laboured or heavy breathing, swim to the top of the tank gasping, gradually becomed lethergic and die if you do not intervene.

You can perfome a water test to ascetain if the pH, ammonia, or nitrite levels are the culprit.

If the results are as expected, perhaps the water from your tap has chemical (chlorine), metals (iron, copper e.t.c), or minerals (too hard or soft), which can be harmful to the fish you have.

To ensure the hygine of your fish tank is not part of the problem, vacuum your substrate, scrape the glass, and clean your aquarium rocks, driftwoods, and decorations regulaly, especially when perfoming a large water change.

Why is Your Fish Spinning Uncontrollably (Vertically, Head Down)

See video in r/aquarium, subreddit

If your fish is spinning uncontrollably, vertically head down, it has whirling disease. Move the affected fish to a quarantine tank immediately, and create a comfortable environment for it before you start treatment.

Sadly, whirling disease is very difficult to treat, and most fish will end up dying from the infection. You can try treating it with Kanamycin, but consider euthanizing your fish if it does respond to treatment promptly because it will only suffer from here on out.

Whirling Disease in Aquarium Fish

Whirling disease is an ailment of freshwater fish caused by the Myxozoan parasite Myxobolus cerebralis. Although the infection is common in wild found fish in the Salmonia family, it is also common with most fish kept in aquariums including discus, corydoras, goldfish, and tetras.

Something noteworthy is that the parasite has two main hosts. It can either be present in the fish itself or freshwater Oligochaete worms, popularly called tubifex.

Infected fish will whirl forward in an awkward, corkscrew-like pattern instead of swimming normally, which happens about 35 to 80 days after the initial infection. The fish also tend to have convulsive movements, increased rate of breathing, and jerking backward movement.

It is quite common for new fish to get infected with the parasite, especially those that come from sellers raising fish in ponds or using tubifex worms as a cheap source of protein for the fish. For this reason, you want to do some due diligence when buying fish from breeders or online.

Susceptability to the disease is influenced by water temperature, age, and species. Young fish are especially vulnerable as the parasite attacks their soft cartilage, resulting in nerve impairment, skeletal damages and sometimes death.


Away from the scenarios explained above, your fish may exhibit other erratic movements, most of which I get questions about.

Below are some of the concerns I get most often.

Goldfish Swimming Erratically

Goldfish swim erratically (or frantically) for the same reasons any fish do. A goldfish will swim erratically when playing, glass surfing, and out of curiosity. However, if you goldfish is swimming erratically after a water change, the new water conditions and quality are likely not ideal, and are nettlesome to your goldfish.

A goldfish swimming frantic and erratically (swimming like crazy) due to water quality is said to be flashing and occurs when your fish is experiencing discomfort on their skin, gills, and fins. The fish will often rub aganist or smin directly into decor and tank wall to scratch and relieve the itching.

Now, a social and interactive goldfish will swim frantically around the tank, mostly in the bubbles from an air-stones, but won’t look stressed or rub aganist surfaces as one suffering from less than ideal water conditions.

If your goldfish is swimming erratically in a corkscrew manner, upside down, or in circles, perhaps its not playing and maybe battling one of the ailments explained above.

Having said that, note that some aquarist refer to the erratic or frantic swimming of a goldfish as darting, which they do when feeling frisky or goofy. However, if your goldfish is (or has been) darting for a while, it is because of the water conditions or quality,including chemicals like chlorine, which you should remedy by doing several water changes over a week.

Why Your Fish is Spazzing Out (Shimmying)

Your fish is spazzing out (having spasms, or shimmying) because of severe stress caused by the your tank water quality and causing your fish to lose control of its nerves and muscles.

If the twitching, shimmyiing, or spazzing is come along with darting motions and swelling, redness, discoloration and heavy breathing, you fish is most likely battling an infection.

For instance, your mollies will spazz out (shimmy) when kept in soft, acidic water.

Even so, some fish, like cichlids shimmy (make spasm-like movements) to flirt and woo mates, and have nothing to do with the water conditions.

Just for perspective…

…the terms spazzing out, twitching, shimmering are often used alternately to refer to spontenous muscular contractions in which your fish’s body moves in a jerky, rapid spasms.

It is an involuntary action where a fish’s muscles tense and relax, especially in the mouth and pectrol fin.

Why Your is Swimming in Jerking Movements (Twitching)

Fish move in jerking motions, twitch or shimmy for the same reasons, water quality. If the water parameters (temp, Ph, Kh, and Gh) or conditions (ammonia, nitrates, nitrites, chlorine, minerals) are not within the range that is acceptable, your fish will swim in jerking motions, shake or vibrate their body.

A jerking fish suffering from poopr water quality may also swim from side to side (with an odd postural trait), calmp its fins (mostly the pectoral fin), shake its head,and experience laboured or heavy breathing.

To remedy (solve) your fish jerking, do frequent water changes and deep clean your fish tank. Test your water with every water change, plus take your water to a lab for a chemical test if you use tap or bore water to refill your tank.

Why is My Fish Swimming Fast Back and Forth

Your fish swimming back and forth or up and down in the tank is called glass surfing and they do this for a number of reasons. Your fish (goldfish) is likely swimming back and forth because of boredom, a visible point of interest outside the tank, issues with water quality or over-crowding; Pigeonscup reddit.

Even so, some fish like betta surf the glass as part of getting used to a new fish tank.

To be sure why your fish is glass surfing, move the items in fish around to see if your fish’s attention shifts. You may also want to test your water incase the parameters are less than ideal for your finny.

Fish Swimming Upside Down

Fish (including betta) swim upside down when they have a problem with the swim bladder, an organ that allows fish to modify its bouyancy according to it’s needs, including to float and dive. A fish will a disorder with the swim bladder may also swim sideways in circles, before it loses balance competely and flip upside down.

Notably, swim bladder disorder is not an ailment, but rather a sign of a underlying issue, hence the best way to deal with it is treating the cause.

Now, while most fish swimming on it’s side or upside down is a sign of injury or death, for finnies like upside-down catfish (synodontis). floating belly up means everything is great and not a cause for concern.

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