Cory Catfish Floating Upside Down: Diagnosis & Treatment

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I can’t stress how worried I was when I saw my cory catfish floating upside down a few years ago. I was sure I was going to lose my fish.

The first step was to research the internet and find out what steps I should take to fix it. But I couldn’t find one source that collects all the important information.

This prompted me to write this article.

Here, I will focus on the well-known swim bladder disease, which is the most common cause of upside-down cory catfish.

Swim bladder disease is the most common cause of a cory catfish swimming upside down.

Why Is My Cory Catfish Upside Down?

The swim bladder is a vital gas-filled organ that maintains buoyancy in fish.[1] Fish use the swim bladder to move freely through the water.

Experts have described the organ as a sac that inflates and deflates according to the needs of the fish.[2]

Swim bladder disease, a condition in which the organ’s functions deteriorate, can have disastrous consequences for a fish’s health.

The Guardian covered a story in 2003 in which the owners of a 17-year-old goldfish placed the creature in a hammock because a crippling swim bladder disorder had ruined the fish’s buoyancy.[3]

Many people thought that euthanizing the goldfish was more merciful than keeping it alive, proving that swim bladder disease is more dangerous than many amateur aquarists realize. 

But death is not the only solution to this ailment. You can cure your cory catfish if you identify and resolve the source of the swim bladder disease before the condition does irreversible damage. 

Prominent causes of swim bladder disease include:

1. Constipation

Constipation has numerous sources, including overeating, poor diets (dry flakes that enlarge the stomach when they expand), physical deformities, low-quality foods, etc. 

Some cory catfish gulp air while eating food at the surface, developing distended bellies in the process. 

Ways To Identify A Constipated Cory Catfish:

  • Bloated body.
  • Distended belly.
  • The fecal matter is long, white, and transparent.
  • The fecal matter hangs from the cory catfish’s anus.
  • No appetite.
  • The catfish will float at the top of the tank.

How To Treat A Constipated Cory Catfish

  • Put the cory catfish on a 3-day fast. This gives the creatures time to digest the food in their stomachs.
  • When the fast ends, feed the catfish a diet of boiled and skinned peas.[4] They act as a laxative. Other notable meal options include cucumber, lettuce, and carrots.
  • Raise the temperature (78-80 degrees F) during the fasting period.[5]
  • Maintain the correct parameters.
  • Use Epsom Salt (link to Amazon) – one tablespoon per gallon. 

Epsom salt is highly beneficial to fish. A paper in The Canadian Veterinary Journal noticed that Epsom salts reduced mortality rates in rainbow trout with diplomonad intestinal parasites.[6]

This is appealing because parasites can cause swim bladder disease. In the case of constipation, Epsom salts act as a muscle relaxant.

Pro tip: Don’t blame every case of bloating on constipation. If the bloating in your cory catfish is accompanied by bulging eyes and scales sticking out like pinecones, the creature has dropsy, which is more dangerous than constipation.[7]

Boiled and skinned peas are an excellent solution when dealing with constipated fish.

2. Bacteria Infection

Bacterial infections are a common source of swim bladder disorders in fish. 

A study from the department of veterinary medical sciences at the Alma Mater Studiorum University of Bologna used diagnostic imaging and bacteriological analysis to explore swim bladder disease in Koi Carp.[8]

They connected the ailment to Aeromonas hydrophila and Shewanella xiamenensis bacteria. These strains enter cory catfish via the gills and wounds on the body.

Ways To Identify Bacterial Infections In Cory Catfish

  • The body will swell because the swim bladder has expanded in response to the infection.
  • Diagnostic imaging will reveal accumulated fluid in the swim bladder and swollen organs.
  • Protruding scales.
  • Loss of appetite.
  • Lethargy.
  • Fin rot.
  • Body ulcers.

How To Treat Bacterial Infections In Cory Catfish

  • Isolate your sick fish and move it to a hospital tank.
  • Remove filter carbons and turn off any UV sterilizers.
  • Add one tablet of Tetra Lifeguard® (link to Amazon) per day to every 5 gallons.
  • Treat for five consecutive days.
  • Repeat the process until the symptoms clear.
  • If present, use water conditioners to neutralize toxins such as ammonia, nitrites, and nitrates.

Bear in mind that the Tetra Lifeguard is a non-antibiotic agent capable of eliminating disease-causing microorganisms.

If you wish to apply antibiotics, consult a veterinarian or an experienced aquarist beforehand. They will guide you away from antibiotics that disrupt the biological filter.

3.  Physical Injury

A physical confrontation between the cory catfish and violent neighbors can injure the swim bladder, leading to infections and inflammation.

Ways To Identify An Injured Cory Catfish

Look for external signs of injury, such as nipped fins, missing eyes, dislocated jaws, cuts, and bruises. External injury may betray internal damage. 

Some swim bladders will swell because of these injuries, resulting in bloating. 

The same thing will happen if the injuries cause the other organs to distend. Those swollen organs will push against the swim bladder, harming it.

How To Treat An Injured Cory Catfish

  • Remove predators, objects with sharp edges, and any other item that can injure a cory catfish.
  • Isolate stressed fish. Put them in a separate container where they can recover in peace.
  • Get the API Stress Coat Water Conditioner (link to Amazon) and add 10 m/L for every 10 gallons of water (this is the recommended dose for damaged skin).
  • Perform regular water changes. 
  • Maintain the correct parameters. An injured fish will heal faster in a conducive environment. 
  • Add antibiotics to prevent infections (only after consulting a vet).
  • Prioritize docile tankmates for cory catfish, including neon tetras, plecos, mollies, shrimp, barbs, guppies, loaches, platies, and snails.
  • Avoid aggressive tankmates, including angelfish, green terrors, oscar fish, male bettas, and parrot cichlids. 
Make sure you remove any sharp objects that could injure your cory catfish.

4. Genetic Deformities

Some cory catfish develop swim bladder disorders because of genetic anomalies and deformities. 

They are not unique in this regard. A paper in ‘Transactions of the American fisheries Society’ investigated swim bladder non-inflation in larval yellow perch. 

Serguisz Czesny (University of Illinois, Urbana Champaign) found that growth rates among yellow perch fell because the fish larvae failed to inflate their swim bladders.[9]

Mortality rates were higher because of starvation and an increased vulnerability to predators.

Another study in ‘Aquaculture’ explored the fate of fish whose swim bladders couldn’t function during the larvae stage.[10]

It also revealed the negative consequences of a defective swim bladder on a fish’s development. 

This shows that swim bladder disease can afflict cory catfish at any stage of their life cycle. 

Maintaining pristine conditions and the correct parameters won’t prevent this ailment if the creatures have genetic anomalies or deformities that plagued them from birth. 

Ways of Identifying Genetic Deformities And Anomalies In Cory Catfish

Genetic deformities typically occur because of interbreeding.[11] They produce physical signs such as a curved spine, bulging eyes, twisted fins and tails, tumors, and more. 

Diagnostic imaging may also reveal swollen organs, including the swim bladder. 

How To Treat Genetic Anomalies and Deformities In Cory Catfish

Unfortunately, you can’t treat these anomalies and deformities. You will probably notice them during the cory catfish’s earliest stages.

It is common practice to euthanize fish in such situations. Although, you can also experiment with invasive procedures if you value your cory catfish’s life. 

The Veterinary Teaching Hospital (College of Veterinary Medicine, North Carolina State University) performed one such procedure on an 800-gram red devil cichlid in 1993.[12]

The creature had buoyancy issues. After using radiographs to identify the enlarged swim bladder as well as kyphosis (spine) and osseous proliferation of the spine, the experts used a celiotomy to approach and reduce the swim bladder’s size.

But the average aquarist doesn’t have the patience or resources to seek out such procedures. 

They are more likely to euthanize cory catfish populations with deformed offspring. Deformities and anomalies caused by infections may respond to anti-bacterial treatments. 

But they don’t always work. For instance, many people use salt to combat bacteria. 

However, researchers published a study in ‘Clinical Veterinary Advisor’ in which they tried to fix a distended and malpositioned swim bladder by increasing the salinity.[13]

They also experimented with repeated pneumocystocentesis. 

But the treatment did not work, and the black telescopic goldfish’s buoyancy suffered. You should consult a vet if you need additional treatment options.

YouTube video of a sick albino cory catfish swimming upside down, probably due to swim bladder disease.

What Else Can Make My Cory Catfish Swim Upside Down?

As previously mentioned, by far the most common cause of upside-down cory catfish is swim bladder disease, which impairs the fish’s buoyancy.

However inappropriate water parameters may also stress your cory catfish and cause it to swim in uncharacteristic patterns, including upside down.

These are the ideal water parameters for cory catfish:

  • Temperature: 72-78° F (22-25° C)
  • pH: 7.0-7.8
  • Water hardness: 3-10° KH
  • Ammonia: 0 ppm
  • Nitrite: 0 ppm
  • Nitrate: Below 20 ppm

It is also worth mentioning that incorrect water parameters can stress your cory catfish and increase the chance of developing swim bladder disease.

Start by checking the basic parameters using a testing kit. 

I personally got the API Water Test Kit (link to Amazon), as it is highly accurate and lasts for hundreds of measures.

The most dangerous finding is an ammonia spike. If this is your case, do not hesitate to check this article, where I explained how to fix it.


If you found your cory catfish upside down, it probably has swim bladder disease, which impairs the fish’s ability to control buoyancy.

There are different causes of swim bladder disease, and each has its own solutions, as I detailed above.

While treating your cory catfish, I highly suggest testing the water parameters with a kit. Fixing those will help your cory fight its underlying condition.