Dropsy in Fish

Ever notice your pet fish looks bloated? They may be suffering from dropsy in fish.

Dropsy is a symptom of a greater health problem in your fish, so it's important to know the signs and catch it early in order to find the best treatment.

What Is Dropsy in Fish?

Dropsy in fish, also known as fish bloat, is when fluid builds up abnormally inside a fish’s body. Fish dropsy is a symptom, not a disease, meaning your fish has an underlying health issue causing the bloating.

There are many potential causes of dropsy in fish, with some being urgent while other reasons may be as simple as poor water quality. If you believe your fish is experiencing dropsy, contact your veterinarian.

Keep in mind that some underlying conditions causing dropsy can be contagious to other fish. If one of your fish exhibits signs of dropsy, be sure to monitor other fish inside the tank as well.

Dropsy in Fish Symptoms

The most obvious symptom of fish dropsy is your fish swelling up with their scales sticking out. Other symptoms may include:

• Swollen belly

• Thickened tail peduncle (stem)

• Protruding eyeballs

• Inability to close mouth

What Causes Dropsy in Fish?

Dropsy occurs when the fish’s kidneys and gills are unable to remove excess water from their bodies. Some potential causes of dropsy in fish may include:

• Poor water quality

• Poor nutrition

• Bacterial infection

• Virus infection

• Severe parasite infestation

• Liver dysfunction

• Cancer (neoplasia)

The most common cause of dropsy is poor water quality, creating a chronic stress situation where the fish’s immune system can no longer function and a secondary environmental bacteria enters the fish, causing kidney dysfunction.

Freshwater fish (goldfish, betta fish, tetras, guppies) have bodies that are denser than the water around them, so water is constantly moving into their body through passive diffusion. This means the fish does not need to use energy to move water in through their gills.

Fish kidneys and gills actively work to pump excess water out of the fish and back into the environment. This process is reversed in saltwater fish.

If these processes stop working properly, either from bacteria or a virus invading the kidneys, tumor compression, or stress elsewhere in the body, water will start to build up in the tissues. This includes the skin—causing the scales to stick out away from the fish’s body.

If the underlying condition can be treated quickly, damage is usually not permanent in the fish. If the condition cannot be treated or if the condition is not treated immediately, the kidneys will be irreparably damaged and the fish will not recover.

Kidney tissue is non-regenerative, so once it is damaged, it cannot be reversed. Gill tissue can regenerate, but will cause more severe disease if damaged.

How Veterinarians Diagnose Dropsy in Fish

Dropsy is one of the few medical conditions that can be diagnosed by veterinarians from observing a fish’s physical appearance.

However, since dropsy in fish can be caused by various underlying health issues, a full workup is critical to diagnose the cause of the dropsy. This may include:

• Water quality testing

• Skin mucus and gill biopsies

• Ultrasound or CT scan with fluid

• Other fluid sample removal with a needle if necessary

Skin mucus and gill biopsies are routine and are used to examine the gill tissue structure and any potential parasites under a microscope. However, this can only give information about the external environment of the fish.

Stained gill samples or any samples taken by a needle may be sent to a diagnostic lab for further diagnosis.

A vet may want to order an ultrasound or CT to look inside the fish, which can show the kidneys and other internal organs. This will help the vet determine if there is a mass or fluid in the organs. A needle may be inserted and a small sample may be taken for further analysis.  

How To Treat Dropsy in Fish

Given dropsy’s many potential underlying causes, it’s critical for a vet to run various diagnostics in order to determine the best possible treatments for your fish’s dropsy.

The best treatment for dropsy in freshwater fish is to take some of the pressure off of the kidneys and gills by increasing the salinity (salt content) of the water. Adding salt can help decrease the amount of water moving into your fish by stalling the process.

Fish species will vary in the amount of salt their bodies can tolerate, so always consult with your veterinarian before you add anything to your tank. Depending on the species, too much salt can be problematic. A minimum level of 0.5 ppt or 0.05% is typically safe.

Never add over-the-counter antibiotics to a tank. This treatment will likely not help and end up killing off the beneficial bacteria, causing an ammonia spike and resulting in more stress on your fish.

Unfortunately, medications to reduce stress in fish have been proven to be ineffective. If you are concerned about your fish with dropsy, call your veterinarian immediately so there is a better chance at recovery.

Recovery and Management of Dropsy in Fish

Once the proper treatment for your fish is identified, fish with dropsy may recover within a few days to weeks. The recovery timeframe depends on the initial cause.

For bacterial infections, the water temperature will determine how fast recovery occurs, with warmer water causing faster recovery. However, this does not mean that increasing your tank water temperature will help your fish heal faster.

It is always best to keep your fish within the correct temperature range for their species.

Swelling will typically decrease from the back of the body forward, so it is recommended to take sequential pictures every day to note the progression of recovery.

If dropsy is left untreated, fish may die within hours or days. They will typically continue to swell, become unable to eat, and suffer from anemia, which will result in organ failure and leave them without enough blood to remove waste from their tissues.

If your fish is not eating or behaving normally, humane euthanasia is recommended, performed by a qualified veterinarian.

How To Prevent Dropsy in Fish

The best prevention strategy for dropsy in your fish is to maintain good water chemistry and ensure your fish is receiving proper nutrition.  

Decreasing stress in fish is the best management for many health issues, including dropsy. You can work to reduce stress in your fish by identifying and resolving:

• Water quality problems—Water quality ranges will depend on your fish species. Test your water quality at least once a month and modify your maintenance routine if anything is out of range.

• Diet and nutrition imbalances—All fish have different dietary requirements, and a varied diet is typically the best option for many fish species. Be sure to replace your containers of food every six months to ensure adequate vitamin levels, and store in a cool, airtight container.

• Tank mate aggression—Some fish species or individuals do not play well with others and can cause chronic stress or trauma. If you note any fish running into each other, it is probably time to move them into their own tank.

• Too little tank space—Most aquariums are overstocked, and this can increase stress on their inhabitants. If you have too many fish in your tank, it can cause severe health issues as they mature.

Be sure to follow strict recommendations when adding new fish to your tank. This is essential to ensure no dangerous bacteria, parasites, or viruses get into a health system of the tank and the fish living in it.