About Dropsy

Names: Bloat, Dropsy
Disease Type: Bacterial or gram-negative
Cause/Organism: Multiple causes, usually stress or environmental


Dropsy is the buildup of fluid inside the body cavity or tissues of a fish. As a symptom rather than a disease, it can indicate a number of underlying diseases, including bacterial infections, parasitic infections or liver dysfunction.


  • Swollen belly
  • Scales stand out
  • Bulging eyes
  • Loss of color/Pale gills
  • Feces pale and stringy
  • Fins clamped against the body
  • Ulcers
  • Loss of appetite

Symptoms vary widely. Some fish present with the classic swollen belly, others display skin lesions, while still others show few symptoms at all. This variability is what makes diagnosis difficult. However, in most cases, a number of symptoms are observed, both physical and behavioral.

These symptoms are the result of the progression of the infection. Internal organs are affected, most notably the liver and kidneys. Anemia occurs, causing the gills to lose their normal red color. As the abdomen fills with fluid organs are pushed aside, sometimes causing the spine to curve. Scales protrude from the body, giving the appearance of a pine cone. This symptom is a classic indication of a severe infection.


The bacterial agent that causes Dropsy is one of several gram-negative bacteria commonly present in aquarium habitats. The underlying cause of fish becoming infected in the first place is a compromised immune system that leaves the fish susceptible to infection. This can happen as the result of stress from a number of factors, such as the following:

  • Poor water quality
  • Ammonia or nitrite spikes
  • Large drop in water temperature
  • Stress from transportation
  • Improper nutrition
  • Aggressive tankmates
  • Other diseases

Generally, a single or short-term exposure to stress will not compromise the ability of the fish to fight infection. In most cases of lowered immunity, the stress exposure has happened for an extended period of time or several stress factors have occurred in rapid succession.


Dropsy is not easily cured. Treatment is geared toward correcting the underlying problem and providing supportive care to the sick fish.

  • Move sick fish to a hospital tank
  • Add salt to the hospital tank, 1 tsp per gallon
  • Feed fresh, high-quality foods
  • Treat with antibiotics

A broad spectrum antibiotic specifically formulated for gram-negative bacteria is recommended, like Mardel Maracyn® 2. Always follow directions for duration and dosage. It is important to move the infected fish to another tank to separate them from the healthy fish. Meanwhile, perform a water change on the original tank and monitor the fish closely for the appearance of symptoms. Salt should be added to the hospital tank at the ratio of one teaspoon per gallon of water. Keep the tank scrupulously clean, and perform weekly partial water changes. Provide a variety of fresh, high-quality food. Often this is enough to resolve the infection in cases that are not advanced. Keep the fish under observation for several weeks after symptoms disappear.


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

  • Perform regular water changes
  • Keep the tank clean
  • Clean the filter regularly
  • Avoid overcrowding the tank
  • Do not overfeed
  • Use flake foods within one month of opening
  • Vary the diet

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

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