Why Is My Fish Swimming Up And Down Erratically? Explained!

Is your fish swimming like it’s drunk or possessed? Distressing, isn’t it?

As a fish parent myself, I would notice that sometimes aquarium fish can behave quite dramatically. And it can be quite worrying to see your pets swimming around like they are writhing in pain or something similar.

So in this post, I will go into the reasons behind fish swimming erratically in an aquarium. I am also sharing corrective measures for fish swimming up and down fast, which you will find very useful, hopefully. 

Fish swimming erratically – what’s happening?

Fish swimming erratically can be a source of concern, especially if you have a relatively calm fish. Here are several reasons why fish swim up and down erratically: 

1. Undergoing stress

For any fish, a change in the water may cause significant levels of stress. Some fishes are very sensitive to changes in water parameters. So fish swimming up and down after water change is very common. 

Even if you don’t change the water, the poor quality of the water can be stressing out the fish. This usually happens when you don’t clean the tank often, and the fish excrement reduces the quality of the water. 

Overfeeding and/or overstocking an aquarium can also stress the fish in a significant manner. 

Here’s what you can do to make sure your fish does not swim erratically due to high stress:

• Always check and test the water before and after changing it in the tank. Test that it has the right level of pH, nitrates, ammonia, and DO
• Frequent cleaning of the fish tank works great. Excess food and mold growth may also stress your fish – so a nice scrub and vacuuming every now and then works wonders. Two to three weeks is usually a sweet spot when it comes to cleaning fish tanks. 
• Try not to overfeed the aquarium fish. Leftover food in the tank starts decomposing and will affect your water parameters.
• Try to curb your enthusiasm in overstocking fishes. If you try to house a lot of fishes in a small tank, it will cause stress to the fishes since they may get aggressive over territories and may not get enough oxygen from the water.

2. Glass Surfing

A new fish may swim up and down in a new home, aka the tank, is also something that you will notice. This is usually called glass surfing or simply pacing the sides of the glass tank.

Often, this is not a cause for concern. But do check if your tank houses enough hiding spots for the new fish.

3. Parasitic infection 

Fishes may swim furiously if they are infected by a parasite. In my experience, a fish with external or internal parasitic infection also keeps rubbing itself on the sides of the tank or decor in the tank.

Here’s what you can do to prevent a fish from swimming up and down due to a parasitic infection:

• Consider introducing anti-parasite slime to get rid of the parasite.
• Adding salt also helps boost the fish’s immune system.
• You may temporarily bump up the water’s temperature to kill the parasites – but do it in small increments, or else your fishes may get shocked due to sudden change in temperature
• Consider quarantining the affected fishes to a different tank
• You may consider using remedies like Imagitarium Parasite Remedy

I also suggest consulting a vet who has expertise in aquatic pets and fish in general. 

4. Your Fish May Be Pregnant

Does it mean fish is pregnant? This is the first question that most fish parents ask when a fish swims erratically.

And yes, it is also one of the reasons why a fish will swim up and down very quickly throughout the day. 

A pregnant fish will also exhibit ‘shimmies’ – swims quickly for some time, followed by an episode of shuddering.

This fish behavior usually happens several times throughout the day. 

Here’s what you should do if you suspect that your fish might be pregnant:

• Keep it under observation and keep feeding a balanced diet
• Check the water for the right temperature and other parameters to nurture the would-be mother fish. 

5. Ammonia poisoning 

Tank fish will also swim erratically due to high concentrations of ammonia in the water. Goldfishes are particularly prone to ammonia poisoning, and they can go round in circles almost constantly throughout the day. 

What should I do?

In my experience, the best remedy for ammonia poisoning is to stop feeding the fish. Additionally, I find that adding a water pump to aerate the tank water also helps significantly. 

Changing the water frequently in small quantities also works wonders. The trick is to stabilize the levels of ammonia and nitrates in the tank to about 0 ppm or around that figure.

6. Your Fish Is Just Exercising

Sometimes when a fish is glass surfing or swimming up and down a lot, it is exploring its playful nature or getting its exercise. Understandably, some species of tank fishes are more playful than others. 

What should I do?

Some species such as bettas are famous for their glass surfing and jumping abilities. The best measure is to provide a sturdy cover on the tank so that the fish doesn’t accidentally leave the tank. 

Other than that, there is nothing you can do about a glass surfing fish other than to enjoy its beautiful display of acrobatic skills. 

FAQ About Fish Swimming Up and Down

Wrapping up 

Fish swimming up and down in a furious manner can be quite stressful for most aquarium owners. However, unless it is a case of parasitic infection, you don’t have to worry about the change in their swimming behavior.

Even then, a water change and a quick trip to the vet should fix the erratic fish behavior in no time.