Fish Floating on its Side

Fish Floating on its Side: Is it Dead?

Most aquarium owners know the alarming sight. You walk in to examine your beautiful fish tank only to see one of your fish strangely floating on its side. 

What is wrong with your fish? Is it dead? It certainly looks that way, since fish don’t ordinarily float on their sides unless something is wrong. However, don’t panic – fish can float on their sides for many reasons that aren’t necessarily related to injury or disease. 

Read on to learn more about why fish float on their sides and the variables that cause it. 

Possible Causes of Side Floating

Why is my fish floating on its side? It’s a question asked by novice aquarium owners and seasoned aquatic hobbyists alike. Admittedly, a fish floating on its side is a strange sight. 

Possible causes of your fish floating on its side are as follows: 

  • swim bladder disorder
  • physical injury or deformity 
  • stress or other environmental factors

Let’s break down each of these variables and why they might cause fish to float on their sides. 

Swim Bladder Disorder

All fish have an organ called the swim bladder, which is filled with gas and helps fish maintain buoyancy  in the water. At lighter water pressures, the gas expands and helps fish float easily to the surface. When the fish dives, the gas contracts, helping the fish descend into deeper waters.

Swim bladder disorder is quite common and can affect many kinds of fish, though some fish are more susceptible to it than others. 

Most times, swim bladder disorders are caused by overfeeding and results in the fish being constipated and unable to float and swim properly. In other cases, swim bladder disorders can be caused by infection, or the swim bladder can become damaged from stress or injury. 

Some fish are more susceptible to swim bladder disorders than other fish species, such as fancy goldfish or betta fish. Keep this in mind when considering either as a pet. 

Physical injury or deformity

Sometimes, fish are born with a deformity – such as an underdeveloped fin – that prevents them from swimming properly.

Other times, side floating can be caused by an injury inflicted by other fish. This is especially common when incompatible fish species reside in the same tank, or if there are two or more males of the same species fighting for dominance. 

Make sure to properly research any fish species you are considering adding to your tank, so as to avoid mixing two species that are incompatible – such as African cichlids and tetras. 

Stress or other environmental factors

If the water quality in your tank is poor, your fish will let you know by exhibiting symptoms of stress. This can include your fish floating on their sides. 

To determine if stress is the cause of your fish’s odd floating position, check your water parameters with an aquarium test kit and make sure the water temperature isn’t too low or too high. 

Stress in fish can also be caused by incompatible species sharing a tank – as one species might be attacking and bullying another – and if there is a lack of shelter in a tank. Most fish need hiding places in the form of rocks, plants, and other decoration to feel safe and secure. 

How to Tell if a Fish is Alive or Dead

If you can’t tell if your side floating fish is alive or dead, the following signs will help you determine whether your fish can be treated or if it’s time to flush it down the toilet. 

  • Gasping for air – if your fish is gasping for air along the water’s surface, this is an indication that your fish is alive and needs to be treated. 
  • Movement – living fish will still have control over their movements, even if they are floating on their sides. 
  • Reaction to stimuli – try touching or moving your floating fish, taking care not to injure it. Fish that are still alive will react to being touched while dead fish will not. 

If your fish is still alive, you’ll need to know how to treat it right away. 

How to Treat a Floating Fish

If you suspect your fish is floating on its side due to an illness or injury, it’s important to seek out the advice of a licensed veterinarian or a fish expert right away. Many pet stores have experts who can offer their advice and the best way to treat your fish, whether it be through medication or improving water quality.

If your fish’s condition is severe, it might require more drastic measures such as surgery. 

If your fish’s strange floating position is due to stress, consider the possible underlying causes. Are there incompatible fish species sharing a tank? This question requires research to answer, but you can also observe the behavior of your fish. Sometimes it’ll be obvious if one fish is bullying or stealing food from another. 

Check your water parameters to make sure the tank doesn’t have a chemical imbalance, such as high ammonia or nitrate levels. Testing for this is easy, as there are test kits you can buy at any pet store. Check the temperature and the pH as well. 

Waste buildup can also cause your fish stress, so make sure to change out your water filter regularly and check if your air pump is running smoothly. A defective air pump affects the oxygen levels in your tank. 

If your fish’s swim bladder disorder is caused by constipation due to overfeeding, the best and easiest solution is to stop feedings for about 3 – 4 days. This will give your fish plenty of time to digest and burn off all the excess food in its system. 


To recap, your fish may float on its side due to stress, environmental factors, injury or illness, or a swim bladder disorder. Know the identifying factors of each and know how to treat each of these causes. 

It’s important to seek out verified information on caring for different types of fish so you can have a happy, healthy aquatic community for years to come.