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Home > Goldfish > Why is My Goldfish Swimming Erratically? Vet-Reviewed Behavior Explaination

Why is My Goldfish Swimming Erratically? Vet-Reviewed Behavior Explaination

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Dr. Luqman Javed

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If you’ve kept goldfish for more than a day or two, you’ve likely noticed that sometimes they do things that seem unusual. It can be challenging to know why they are behaving oddly, though. One of the more common unusual behaviors you may see your goldfish exhibiting is frantically swimming around the tank, but is this something you should be concerned about? To better understand this behavior, you need to understand what can cause it.

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Goldfish Play

One of the most common causes of erratic swimming in goldfish is simply play. Goldfish are far more social and interactive than they are often given credit for, so it’s not uncommon for goldfish to be spotted rapidly swimming around the tank when they’re feeling playful.

Some goldfish may even play in the bubbles from air-stones and the currents from filters, while others may shoot from end to end in the tank as quickly as they can. In general, goldfish prefer tanks that are longer than they are tall so they can stretch their fins, so to speak, and swim end to end.

A mostly white lionchu goldfish looking right into the camera
Image By: Sardo Michael, Shutterstock

Goldfish Flashing

Flashing is not a disease, but it is a sign of a disease or problem with water quality. Goldfish experiencing discomfort on their skin, gills, or fins may rapidly and erratically swim around their tank, often rubbing against or swimming directly into décor and the sides of the tank. This behavior may help relieve itching or discomfort by scratching or rubbing against things in much the same way we might scratch an itch or rub a sore spot.

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Causes of Flashing

There are a variety of problems that can lead to flashing. Poor water quality or rapid changes in water parameters can cause great discomfort for your fish. The presence of ammonia and nitrites in the water can lead to flashing, as can elevated nitrate levels. Rapid changes in pH and temperature can cause discomfort for your fish and cause erratic swimming patterns. A pH level that is too low can also cause discomfort for your goldfish since they prefer water that is close to neutral.

Another very common cause of flashing in goldfish is parasitic and fungal infections. Ich, anchor worms, and gill flukes can be uncomfortable for your goldfish, leading to them attempting to scratch itches by flashing. Some fungal infections can also lead to discomfort, especially as they begin to cause deterioration of the skin, gills, or fins, which can also cause your fish to flash.

wakin goldfish in a tank
Image By: JuanCarlosPalauDiaz, Shutterstock

Swim Bladder Problems

Goldfish have an organ called a “swim bladder” that helps them control their buoyancy. Some fish may experience dysfunction of this organ, with fancy varieties of goldfish being the most prone in the world of goldfish. When goldfish are experiencing swim bladder dysfunction, they may swim erratically because they are unable to properly control their buoyancy. This can lead to them moving in unusual ways, including swimming in circles and upside-down.

Mating Behavior

Goldfish may also appear to swim “erratically” as part of their mating pattern. During the mating season, the male goldfish typically chase females around in an almost obsessive fashion, resulting in what appears to be a cat and mouse scene in spawning pools. Males also develop white spots on their face during this time, which many inexperienced owners mistake for ich.



Most goldfish may swim in an unusual or erratic pattern as part of their playtime. However, some goldfish will swim erratically when they are flashing due to discomfort or experiencing dysfunction of their swim bladder.

If your goldfish suddenly begins exhibiting erratic swimming patterns, the first thing you should do is check the water parameters to ensure everything is at safe levels. Make sure to dechlorinate water before adding it to the tank and wait for the temperature to reach the same temperature as the tank before adding it.

If your water parameters are in order, closely examine your goldfish for evidence of parasitic or fungal activity, like white patches, flecks of white, sand-like materials, or redness. You can also prophylactically treat with an antiparasitic or antifungal if you believe you’re dealing with one of these issues, although this is not advisable if your goldfish appears healthy.

Once you’ve ruled out other problems, just keep an eye on your goldfish’s behavior. This may be normal behavior for your fish, and they may just be showing you their playful nature and how happy they are to be in their home.

Featured Image Credit: Pavaphon Supanantananont, Shutterstock

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