Hidropisia em peixe de aquário

Dropsy in aquarium fish


Dropsy, also known as water belly, is an acute and serious infection. It is a syndrome where fish have an extremely swollen belly, due to the accumulation of water and other fluids, due to the gradual failure of the kidneys.

Check here the causes, symptoms and treatment options for this condition that can affect your fish.

A disease of immunocompromised fish

Dropsy is caused in most cases by bacteria commonly present in all aquariums. However, it can also come from protozoa, viruses, genetic propensity and exposure to poor water conditions for a medium/long period.

Any fish inside the aquarium will be exposed to the bacteria that causes dropsy, but healthy fish rarely fall victim to the disease. Fish are only susceptible when their immune system has been compromised.

If all the fish are under stress, it is quite common for all of them to become infected, but it is also possible for just one or two fish to become sick, especially when immediate action is taken to prevent the spread of the bacteria.

Signs of dropsy in aquarium fish

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

Bacterial infection symptoms can vary widely. Some fish, for example, have the classic swollen belly, others have skin lesions, while others have few symptoms. This variability is what makes diagnosis difficult. In most cases, a series of symptoms are observed, both physical and behavioral.


  • Very swollen belly;
  • Ruffled scales;
  • Eyes bulging;
  • Pale gills;
  • The anus that becomes red and swollen;
  • Clear and sticky stools;
  • Ulcers on the body, along the lateral line;
  • Redness of the skin or fins;
  • General lethargy;
  • Refusal to eat;
  • Constantly swimming close to the surface.

These symptoms occur progressively as the disease progresses. Internal organs are affected, mainly the liver and kidneys. Anemia occurs, causing the gills to lose their normal red color. As the abdomen fills with fluid, organs are pushed to the side, sometimes causing the spine to curve. Scales protrude from the body, giving it the appearance of a pine cone. This symptom is a classic indication of serious infection.

Causes of dropsy

The agent that causes the symptoms of dropsy is usually the bacteria Aeromonas, one of several gram-negative bacteria present in most aquarium habitats.

The bacteria will only cause serious infections in fish that already have compromised immune systems. This can happen as a result of stress from a number of factors, such as:

  • Poor water quality;
  • Ammonia or nitrite spikes;
  • A large drop in water temperature;
  • Transport stress;
  • Inadequate nutrition.

Generally, a single or short-term exposure to stress does not compromise the fish’s ability to fight infection. Only over a long period of time is the fish’s immune system affected.


The infection that causes dropsy is not easily cured. Some experts recommend that all affected fish be euthanized to prevent spreading the infection to healthy fish. However, if the infection is detected early and the fish are isolated for proper treatment, it is possible to save the affected fish. Treatment is aimed at correcting the underlying problem and providing supportive care to sick fish:

  • Move sick fish to a “hospital tank.”
  • Feed your fish fresh, high-quality food.
  • Treat fish with antibiotics, whether in food or water.
  • Test the water in the hospital tank daily to ensure it is suitable for the fish.

It is important to move any infected fish to another tank to separate them from the remaining healthy fish. While the affected fish are quarantined, perform a water change in the original tank and monitor the remaining fish closely for the appearance of symptoms.

How to prevent dropsy

As with many illnesses, prevention is the best medicine. Almost all factors that stress fish enough to make them susceptible to infection can be avoided. Check out a list of items that need your attention:

  • Test your aquarium water regularly to ensure it is healthy for your fish;
  • Perform regular water changes;
  • Keep the aquarium clean;
  • Clean the filter regularly;
  • Remove residues from the bottom of the tank;
  • Do not add more fish than the aquarium can hold;
  • Do not overfeed your fish.

If the aquarium is well maintained and the fish have a healthy diet, infections that cause dropsy are unlikely to develop.

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