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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.
4 Reason Why Your Fish Might Be Swimming Erratically (Abnormally)
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.
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.
Whirling Fish Disease
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.