Why Does My Fish Swim Sideways? Causes And Prevention

Estimated read time 7 min read

In this article,  we’ll answer the question: Why Does My Fish Swim Sideways and explain why it’s happening and how you can prevent it.

It’s not easy figuring out what’s wrong with a fish. It’s not like you can feel their forehead and see if they have a fever.

Is it sick? Hungry? Sad?

Sometimes, your fish is just fine. Other times, there is definitely something wrong with your scale, baby, and you need answers – fast.

Have you noticed your fishy is swimming a little… oddly? Maybe it’s been swimming upside down or on its side? We know precisely what that means and how to fix it.


Why Is My Fish Swimming Sideways?

A fish that is suddenly swimming sideways or upside down usually has what is known as “swim bladder disease.” The swim bladder is an internal organ that most bony fish have. It’s a gas-filled sac that sits behind the other internal organs and controls the fish’s buoyancy.

Basically, it’s a gas bag that allows the fish to control its position in the water. If you are familiar with scuba diving, you could like it to a buoyancy control device (BCD).

The swim bladder, also used for sound detection and production, is essential to your fish’s overall wellbeing.

A fish suffering from swim bladder disease can’t regulate the gas going in and out of their swim bladder, which causes an imbalance and makes them float on their side or upside down.

What Is Swim Bladder Disease?

Swim bladder disease, or SBD, is a disease that a fish may suffer from when its swim bladder is compacted. When this happens, the fish can’t hold air in the correct areas, resulting in the fish swimming upside down or on its side.

Betta fish and fancy goldfish are most often affected by SBD because of their shape and spine structure. Round, short bodies are more likely to have compressed organs, making it difficult to digest food, leading to constipation.

Be wary of SBD in these breeds of fish and prepare accordingly (check out our tips on preventing SBD below!).

What Causes Swim Bladder Disease?

Swim bladder disease isn’t some random cold your fish catches in the winter: SBD has causes (and solutions!).

There are multiple causes, and it’s crucial to determine what exactly happened so you can prevent it from happening in the future.

Swim bladder disease (some refer to it as swim bladder disorder) is largely caused by overfeeding (which then leads to bloating and constipation) or an infection (probably from a dirty tank). It can also be caused by taking in too much air when the fish bites at food.

Causes Of Swim Bladder Disease Include:

Constipation and metabolism issues

When a fish is constipated or has metabolism issues, the fish’s swim bladder is compressed, making it too full, which changes the buoyancy.


The high nitrate levels in the food can easily lead to bloating and constipation if the fish are overfed, leading to SBD.

Bacterial infections or parasites

Not keeping a clean tank is one of the leading causes of bacterial infections and parasites.

Enlarged organs and blockages

These can occur when fish swallow too much air. Some rare defects cause enlarged organs or blockages, though these usually show up early in the fish’s life.

Cool water temperature

Coldwater slows down your fish’s metabolism, causing constipation and other digestive issues that can lead to SBD.

Can Swim Bladder Disease Be Cured?

Thankfully, you can cure swim bladder disease if you catch it early on, but it’s not something that’s healed with medicine.

First, you need to put your fishy friend on a strict, no-food diet for three-to-four days. Fasting will allow whatever metabolism issues your fish has to sort themselves out.

On the fourth or fifth day, feed your scaly friend a cooked pea (no skin!). This will help ease any constipation and clear out the system. You can microwave or boil a pea and squeeze off the skin once it’s cooked.

Keep your fishy friend’s aquarium water between 78-80°F. This will help regulate your fish’s metabolism and keep them comfortable.

It’s also not a bad idea to lower your fish tank’s water level a little while they are recovering. It will make it less stressful for your fishy friend to swim around and get their food. Plus, the filter will clean up any excess gunk faster and easier.

How Do I Prevent Swim Bladder Disease?

The best medicine in this case (and most cases) is prevention. The two most vital factors to remember are water quality and proper feeding.

Dirty tanks are the main cause of infections and intestinal parasites, which is why it’s so important to keep your tank clean. Net out any excess food or debris you notice in the tank to extend your filter life and give it a break.

Overfeeding causes constipation and bloating, so take care to feed your fish the appropriate amount. The general rule is to feed your fish only what it can eat within 2-3 minutes.

If you’re feeding dry food, take a minute to wet it before giving it to your fishy friends. They won’t have to gulp in as much air if the food is already soaked.

Unless otherwise noted for your breed of fish, the ideal temperature is 75-80°F (Degrees Fahrenheit).

Could It Be Anything Else?

For this particular symptom, it usually isn’t another malady. However, fish can swim erratically (darting around, swimming in circles, etc.) for several reasons. If your fish is acting strangely, talk to your vet or an aquatics care specialist.

Video: How to treat a floating bloated Goldfish with a swim bladder disorder with Dr. Loh Fish veterinarian.

So, Now What?

If your fishy friend is swimming funny, don’t panic. Follow these steps, and your friend will be on the boat road to recovery.

  1. Don’t feed them for 3-4 days.
  2. After the fasting period, please give them a cooked, shelled pea.
  3. Keep their water temperature at 78-80°F during the recovery period.
  4. Lower their water level during the recovery period.

If you haven’t had a run-in with swim bladder disease, take some preventative measures and make sure your fishy friend’s home is clean, the right temperature, and you are feeding them the appropriate amount.

If you have encountered SBD before, leave a comment! Did you use the same treatment, or do you have other tricks up your sleeve? Let us know!

Further Reading: Most Popular Freshwater Aquarium Fish


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