Dropsy in Fish: Signs, Treatment, Recovery

A Bacterial Infection Known to Cause Fish Bloating

Dropsy in a betta

Clintus / Flickr / CC by 2.0

Dropsy refers to the swelling of soft tissues in a body cavity, such as the abdomen, due to an accumulation of water and other fluids. The condition is caused by environmental stress factors and/or infections. Though it's extremely difficult, it is sometimes possible to treat and cure dropsy and the associated diseases in fish when it's caught early—especially if the affected fish can be isolated.

What Is Dropsy?

Although the term dropsy is rarely heard in human medical science these days, it is still used to describe a particular health issue with aquarium fish. Dropsy is more typically called edema or ascites today; it refers to a condition in which fish often have hugely swollen bellies. The continuing use of the term probably has to do with how it so accurately depicts the visual symptom of a dropped-down belly. Sometimes the condition is also known as bloat.

Symptoms of Dropsy in Fish

As the infection progresses, skin lesions may appear, the belly fills with fluids and becomes swollen, internal organs such as the liver and kidneys are damaged, and ultimately the fish will die if the disease is advanced.

Symptoms

  • Grossly swollen belly
  • Scales with abnormal appearance
  • Bulging eyes
  • Pale gills
  • Swollen or red anus
  • Pale or stringy feces
  • Ulcers
  • Curved spine
  • Clamped fins
  • Redness of the skin or fins
  • Lethargy
  • Refusal to eat
  • Swimming near the surface

Grossly Swollen Belly

A fish with dropsy will appear like it is ballooning and about to explode, or it has a pot-bellied appearance that makes it seem like it's suddenly getting very fat. This happens as fluid accumulates in the tissues and cavities of the abdomen to create swelling of the area. Both the kidneys and spleen are also swollen because they are shutting down and can't eliminate the water build-up from the fish's body.

Scales With Abnormal Appearance

The internal swelling will affect how a fish's scales lay on the body. With dropsy, scales are no longer flush on the body. Instead, they will protrude and point away from the skin, giving the fish an overall pinecone appearance. This dropsy symptom is a classic indication of a severe infection.

Bulging Eyes

A fish with both eyes bulging may have popeye disease as a result of an infection. The swollen eyes are occurring because the organs are shutting down and creating an excess of fluid that is leaking around the tissues and can't be eliminated from the body. The fluid is causing pressure behind the eyeball area resulting in deformation.

Pale Gills

The infection or disease resulting in dropsy will also cause anemia to occur in the fish, resulting in the gills losing their normal red color.

Swollen or Red Anus

If your fish has the bacterial "enteric redmouth disease," it will have a swollen and red anus, as well as other parts of it its body. This symptom accompanies other signs of dropsy.

Pale or Stringy Feces

If your fish has an infection, and has other dropsy symptoms, it probably won't eat. Pale feces is feces without food. In addition, your sick fish will secrete more mucus than actual feces. What will come out of its body will appear pale and stringy.

Ulcers

A fish with dropsy may have a severe bacterial skin infection which can cause ulcers. The ulcers will typically form along the lateral line of the body

Curved Spine

As the abdomen fills with fluid, organs are pushed aside, sometimes causing the spine to curve.

Clamped Fins

A sick fish will often have clamped fins (fins held abnormally tight to the body). It may clamp its fins because it is difficult to move them if its body is very swollen, distended, and in pain.

Red Skin/Fins

If your fish has an Aeromonas infection, which causes signs of dropsy, it will be hemorrhaging on or under the skin and create an appearance of bloody red skin and red fins.

Lethargy

There are many reasons why a fish will be listless, but having a disease plus other symptoms of dropsy will certainly be exhausting. The fish's organs and its body, in general, are not fully functioning.

Refusal to Eat

A fish with dropsy will stop eating due to discomfort and dysfunctional organs. You may see your fish trying to hide in aquatic plants or structures because it does not feel well and it is not interested in food.

Swimming Near the Surface

A lethargic fish with dropsy may hover at the bottom of the tank or hide, but it can also swim near the top, too. This may be because the fish has lost its ability to properly swim and it cannot maintain its natural buoyancy.

Gif showing the symptoms of dropsy in aquarium fish

The Spruce / Kelly Miller

Causes of Dropsy

The agent that causes the symptoms of dropsy is usually the very common Aeromonas bacteria, one of several Gram-negative bacteria present in most aquarium habitats. The bacteria are known as Gram-negative because they do not take on a specific stain used in the Gram stain method of identifying bacteria species.

The bacteria will only lead to a serious infection in a fish that already has a compromised immune system. This can happen as the result of stress from several factors, such as:

Generally, a single or short-term exposure to stress will not compromise the ability of the fish to fight infection. In most cases, the stress exposure must be present for an extended period, or several stress factors must occur in rapid succession to affect the fish's immune system.

Diagnosing Dropsy in Fish

Symptoms of the underlying bacterial infection can vary widely. In addition, oftentimes dropsy and swim bladder disorder are confused upon diagnosis because both conditions display similar symptoms, such as distended bellies, curved spines, and general malaise. Some fish with dropsy will have the classic swollen belly, others display skin lesions, or show few symptoms at all.

This variability in symptoms makes the diagnosis of dropsy difficult. In most cases, a number of symptoms are observed, both physical and behavioral. However, your veterinarian will likely need to do lab tests to figure out what type of infection the fish has to determine the type of antibiotic to use.

Treatment

If the infection is detected early and the fish are isolated for proper treatment, it is possible to save the affected fish. Treatment is geared toward correcting the underlying problem and providing supportive care to the sick fish. Here is a list of treatment steps to take:

  • Quarantine: Move the sick fish to a "hospital tank." It is important to move any infected fish to another tank to separate them from the remaining healthy fish.
  • Add salt: Add 1 teaspoon of salt per gallon of water to the hospital tank. Low levels of salt in the water aid in the osmotic balance of the fish by making the water salinity closer to the fish's blood salinity. That helps the fish get rid of excess water accumulating in the body, causing dropsy. But, don't add too much salt as that can be unhealthy for freshwater fish.
  • Clean water: Keep the hospital tank scrupulously clean, and perform weekly partial water changes, adding salt to the new water being added to the aquarium. Test the water in the hospital tank daily to ensure it is appropriate for the fish.
  • Food: Provide the ill fish with a variety of fresh, high-quality food. Often this is enough to resolve the infection in cases that are not too far advanced if the fish is still eating.
  • Antibiotics: Treat the fish with antibiotics, either in the food or in the water, if the fish does not immediately respond. A broad-spectrum antibiotic specifically formulated for Gram-negative bacteria is recommended, such as Maracyn-Two. A 10-day course is ideal for ensuring the infection is eradicated, but you should always follow the manufacturer's directions for duration and dosage.
  • Observe: Keep the fish under observation for several weeks after the symptoms disappear.
  • Maintain the main tank: While the affected fish are quarantined, perform a water change on the original tank and monitor the remaining fish closely for the appearance of symptoms.

Prognosis for Fish With Dropsy

The disease or infection that is causing dropsy is not easily cured. Some experts recommend that all affected fish be euthanized to prevent the spread of the infection to healthy fish. The outcome is especially bleak for a fish with both popeye and dropsy.

Even with prompt treatment, the mortality rate is high, but your fish can survive. Successful treatment can be highly unlikely unless a fish is diagnosed in the early stages of the infection.

How to Prevent Dropsy

As with many diseases, prevention is the best cure. Almost all the factors that stress fish enough to make them susceptible to infection can be prevented. Because poor water quality is the most common root cause of stress, tank maintenance is critical. Factors to keep in mind include:

  • Test the aquarium water regularly to ensure it is healthy for your fish.
  • Perform regular water changes.
  • Keep the tank clean.
  • Clean the filter regularly.
  • Use a gravel vacuum to remove wastes from the bottom of the tank.
  • Avoid overcrowding the tank.
  • Do not overfeed fish.
  • Use flake foods within one month of opening the packages.
  • Vary your fish's diet.

If the tank is well maintained and the fish are fed a healthy diet, outbreaks of infections causing dropsy are unlikely.

Is Dropsy Contagious to Other Fish?

Since dropsy symptoms are caused by bacteria commonly present in all aquariums, any fish may be exposed to the dropsy-causing bacteria. Fortunately, healthy fish rarely fall prey to the disease.

Fish are only susceptible when some other stress factor has compromised their immune system. If all the fish in the tank are under stress, it’s pretty common for the entire tank to become infected, but it is also possible for only one or two fish to fall ill, especially when prompt action is taken to prevent the spread of the bacteria.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dropsy in Fish. National Cooperative Extension.

  2. Diagnosis and Treatment of “Aeromonas hydrophila” Infection of Fish. Purdue University and University of Illinois Cooperative Extension Services.