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Dropsy, Swim Bladder Disorder & Popeye in Aquarium Fish

Dropsy, Swim Bladder Disorder & Popeye in Aquarium Fish

Just like us, fish are no stranger to occasionally feeling a little under the weather. Unfortunately, when a fish becomes stressed, they are more susceptible to illness. Fish illness, disease and infections are something that many aquarists may encounter at some point during their aquatic journey.


Dropsy is one of the illnesses that an aquarist might run into while in the aquatic hobby. Dropsy is more of a symptom and condition of the illness than the disease itself and is an infection caused by the bacteria Aeromonas. This is a gram-negative bacterium naturally found in aquatic environments. One of the most recognizable symptoms is swelling in the belly caused by a buildup of fluid within the tissue. This swelling can be so severe that is causes the scales to protrude, giving an appearance like a pinecone. The swelling is not always located in the belly, and you may notice swelling in other areas prior to the belly showing signs. Other signs include a paleness around the gills, body lesions and ulcers, loss of appetite, and lethargy.  

This illness is typically caused by consistent stress within the aquarium and/or fish. Because Aeromonas bacteria is naturally present, a continuously stressed-out fish whose natural immune system has become weakened is the most susceptible. These are a multitude of stressors that can negatively affect your aquatic life single-handedly or in conjunction with one another. Poor water quality is one of the most contributing factors not only to bacterial infections but parasitic and fungal infections as well. Maintaining great water quality is one of the best ways of ensuring that the immune system of your fish is at its peak performance. Nutrition is another contributor; making sure your fish are receiving a well-balanced diet will help fight off diseases and keep them happy and healthy. Unruly tankmates can stress everyone out- no fish wants to be bullied and chased around the aquarium all day.  

With any disease, quick identification and treatment is the key to a successful recovery although dropsy is a difficult disease to reverse and may have a poor outcome. If caught early, it is best to move the ill fish to a separate quarantine aquarium for treatment. This will prevent the illness from spreading to other healthy aquatic life. After the infected fish has been removed ensure that the main aquarium receives a water change and routine maintenance is established.  

A salt treatment can also be effective for less advanced stages. Using 1 teaspoon for every gallon of aquarium water will assist in reducing the water retention that is taking place in the fish’s body. Keep the water quality maintained by performing weekly water changes and do not forget to add 1 teaspoon of salt for every gallon that is being replaced. Keep the fish in the hospital system observing it for two weeks after all symptoms of the disease have dissipated. If the salt treatment is not providing favorable results and the disease continues to advance, the use of an antibiotic treatment may be needed. Always follow the treatment instructions provided by the manufacturer.  

Unfortunately, if the illness is severe and the fish is not responding to treatment it may be more humane to euthanize.

Swim Bladder Disorder

Boney fish maintain their buoyancy and posture through an internal gas filled organ, often referred to as the swim bladder. This organ is flexible, allowing it to expand or contract based on ambient pressure. The swim bladder has a big job and is unfortunately not immune from succumbing to disease.  

Just like dropsy, swim bladder disorder can be brought on by poor water quality. Poor water quality can trigger stress and if the stress is constant, it can make fish susceptible to disease. Disease can create inflammation within the organ. Injury from fighting or hitting something within the tank hard enough can also cause swim bladder complications. Additionally, gulping air, overeating and constipation can cause stomach swelling or enlargement of the intestinal tract affecting the swim bladder. In rare incidences, this can happen due to deformities or birth defects. 

One of the obvious signs of a swim bladder disorder is a fish’s inability to right themselves- floating upside down or floating to the top of the tank no matter how much they try swimming downward. However, it does not always involve floating as this disorder also involves sinking to the bottom of the tank. Many fish maintain a normal appetite, but they may refuse to eat. They may also show signs of a swollen abdomen. 

Because of the difficulty of determining what caused this disorder, it may be a little complicated to treat. Depending on the severity, your fish can still live a happy life with this condition but may need a little more hands-on attention. If your fish still has the ability to swim normally you may need to slow the water flow within the tank. If it is still eating, hand feeding may be needed to ensure your fish is getting the proper nutrition they need.  

If you suspect it is disease related, the use of medication such as a broad-spectrum antibiotic may be needed.  

Due to the complexity of a swim bladder disorder, if the condition is severe and your fish is not responding to treatment or accommodation it may be more humane to euthanize to prevent suffering.


Popeye is a disease medically known as exophthalmia which can cause the eye of fish to swell or bulge out. Although a concerning condition, don’t get popeye confused with fish that have naturally protruding eyes like, Telescope Ee or Black Moor Goldfish.  

Like other diseases, the earlier you can diagnose it the better. Some early signs of concern are hiding and loss of appetite. With popeye, it might not be easy to detect early because the eyes may not show any significant extension initially, and the eyes may appear clear. But slight swelling can turn into significant swelling and cloudy eyes in a few days.  

It is not a “one size fits all” cause, as with many diseases, popeye can be caused by various sources. Stress and poor water conditions can cause the fish’s natural immune system to break down, opening it up to infection. Both eyes showing signs of swelling is a good indicator this is driven by an infection. Fish that are fighting off other diseases, like dropsy, can be susceptible to swelling behind the eye as well.  

Popeye may not always be caused by an infection. Fish do not have eyelids and are sensitive which means they can be injured by décor or other aquatic life. If only one eye is experiencing signs of swelling this may be an indicator of injury and you may be able to see the scratch or damage to the eye. In less severe cases, popeye is not typically fatal but permanent damage and loss of sight is possible if left untreated. Additionally, significant swelling can cause the eye to rupture.  

Determine what caused the popeye and ensure your water parameters are stable. A water change can be helpful in addressing any abnormal parameters. The use of aquarium salt will help reduce swelling and aid the fish while the eye injury heals, but you will want to watch closely to ensure a secondary infection does not set in. 

If you have determined that the popeye was caused by an infection and is isolated to a single fish, move the infected fish into a hospital aquarium for treatment. A food based broad-spectrum antibiotic is one of the most effective ways to treat this aliment. If multiple fish are exhibiting signs of illness, you may want to proceed with treating the entire aquarium.    

An ounce of prevention is worth a pound of cure. Preventing diseases through proper water quality, maintenance and providing optimal nutrition are some of the best ways to keep your aquatic life happy and healthy.

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