Dropsy in Aquarium Fish

Dropsy is an old medical term for a medical condition that today would be more likely called edema—the swelling of soft tissues in a body cavity, such as the abdomen, due to an accumulation of water and other fluids. The English term derives from the Middle English word dropesie, from the Old French word hydropse, from the Greek word hydrops, which is itself a derivation of hydro, meaning water.

Symptoms of Dropsy in Aquarium Fish
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. Fish suffering from dropsy often have hugely swollen bellies, and the continuing use of the term probably has to do with how it so accurately depicts the visual symptom: the belly drops down. Sometimes the condition is also known as bloat.

A Disease of Immune-Compromised Fish

Dropsy in fish is actually a cluster of symptoms caused by an infection from a bacteria commonly present in all aquariums. Consequently, any fish may harbor the dropsy-causing bacteria, but healthy fish rarely fall prey to the disease. Fish are only susceptible when their immune system has been compromised by some other stress factor. If all the fish in the tank are under stress, it’s quite 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.

Signs and Symptoms of Dropsy

As the infection progresses, skin lesions may appear, the belly fills with fluids and becomes swollen, internal organs are damaged, and ultimately the fish will die. Even with prompt treatment, the mortality rate is high. Successful treatment is very unlikely unless a fish is diagnosed in the early stages of the infection.

Symptoms of the underlying bacterial infection can vary widely. Some fish will have the classic swollen belly, others display skin lesions, while still others show few symptoms at all. This variability is what makes diagnosis difficult. In most cases, a number of symptoms are observed, both physical and behavioral. These may include:

Grossly swollen belly
Scales that stand out with a pine cone-like appearance
Eyes that bulge
Gills that are pale
The anus that becomes red and swollen
Feces that is pale and stringy
Ulcer on the body, along the lateral line
A spine that is curved
Fins clamped together
General lethargy
Refusal to eat
Swimming near the surface
These symptoms occur progressively as the disease advances. 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.