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Dropsy is a common fish disease that can be found in all types of aquarium fish. Learn how to spot the disease and how to treat it early to give your fish the best chance of survival. 

Goldfish with dropsy

If you have a freshwater aquarium, the last thing you want is for your fish to get sick. It’s important to keep good water conditions in your fish tank to ensure that your fish remain healthy and to monitor the behavior of your fish for any early signs of illness. 

It is your responsibility to stay on top of your fish’s health and make sure your tank is properly operating. Unfortunately, there are so many fish diseases that you must keep track of, and the bacteria that cause these diseases can occasionally sneak into your tank, even with diligent care. 

One of the most common fish conditions that can be found in aquariums is dropsy. This condition can cause your fish’s belly to swell and, by the time it is detected, may be fatal. However, if you notice the disease early and treat it immediately, your fish has a fair likelihood of recovery.

Read on to learn about what exactly dropsy is, what symptoms to look out for, and how to treat your affected fish if they develop dropsy.

What is Dropsy Disease?

Dropsy is the swelling of soft tissue in the fish’s body cavity. This swelling is caused by the accumulation of fluids in the fish.

Dropsy itself isn’t a bacterial disease but a condition caused by a bacterial infection that leads your fish’s body to swell. It can indicate other underlying conditions, such as bacterial or parasitic infection or liver dysfunction. Dropsy is especially common among goldfish, but the condition can affect any freshwater fish in your aquarium, including bettas.

Fish dropsy is usually caused by a number of other symptoms that end up compromising a fish’s immune system. Although many fish can be exposed to the bacteria that cause dropsy, they rarely affect fish with healthy immune systems. 

What Causes Dropsy?

The bacteria that causes dropsy is called Aeromonas and is commonly found in most freshwater fish tanks. Fish are therefore always exposed to the bacteria, but it will only lead to a serious infection in a fish that already has a compromised immune system. Aeromonas bacterium is a “gram-negative” bacteria because it can be identified with a gram staining technique.

The main problem that can affect your fish’s immune system is stress. At times, it could just be one fish in your tank that is feeling stressed in the environment that shows symptoms of dropsy. For example, a fish could accidentally bump into something, causing it to be physically injured and consequently stressed, leading it to be more susceptible to disease.

However, if you notice that more than one of your fish is exhibiting symptoms of dropsy, then there is something wrong with your tank or a common element that is causing stress in all of your fish.

Factors that can cause stress in your fish include:

  • Poor water quality creating an environment for bacteria to thrive
  • Detectable traces of ammonia and nitrate in the aquarium water
  • Poor nutrition (overfeeding, underfeeding or feeding fish poor quality foods)
  • Overcrowding
  • A drastic change in or wrong water temperature
  • Aggressive fish bullying other fish
  • Transportation of a new fish to your fish tank

Dropsy can also happen when your fish’s internal organs have problems, like poor kidney function due to absorbing too much water. 

Symptoms of Dropsy in Aquarium Fish

Unlike other fish diseases, dropsy is generally easy to spot. If your fish develops a huge swollen belly, that’s a good indicator that they may have dropsy. However, if your fish gets too far into this stage, it may be more difficult to treat dropsy as the swollen belly may indicate that your fish’s internal organs are damaged. 

Like other diseases, it’s best to notice that something is wrong before your fish shows any outward symptoms. Before dropsy causes a visible swelling in your fish, it may cause your fish to appear lethargic, and they may eventually lose their appetite and stop eating for a few days before their belly starts to swell. 

Behavioral symptoms to watch out for include:

  • Refusal to eat
  • Swimming near the surface of the tank
  • Listlessness
  • Flashing
  • Clamped fins

As the disease progresses, your fish may develop skin lesions, or fin rot, and their internal organs such as the kidney or liver may be damaged. Fish who have dropsy also often have popeye–a condition which causes one or both of the fish’s eyes to discolor and bulge from their head. 

Your fish may also show signs of discoloration, a swollen anus, pale gills, or a curved spine. In severe cases, the fish’s scales may protrude from the body like pinecones, almost to the point of falling off. Symptoms progress aggressively, so if you notice one, act right away.

Unfortunately, some fish may show no outward systems at all, making this disease difficult to detect before it becomes fatal.


Since stress is the main factor that causes dropsy, the best way to prevent the condition from appearing in your fish is by minimizing factors that may increase their stress levels. Potentially dangerous bacteria are always present in your aquarium–they’re just waiting for a moment of weakness in your fish’s health to strike and do their work. 

Almost all of the factors that can cause stress to your fish, and eventually dropsy, can be prevented with some care and attention from your part. Follow these tips to make your aquarium a stress-free environment for your fish:

  • Keep up with the water quality of your fish tank by performing water changes as necessary so as to not create a suitable environment for bacteria to breed. Be sure to change the water in your tank regularly and make sure the filter is always clean and running properly. Regularly test the water and monitor the temperature. Use a gravel vacuum to remove waste buildup at the bottom of the tank (caused by uneaten food, scales, and feces).
  • Feed your fish a healthy diet of high-quality foods. Make sure the fish food you feed them is not expired to ensure they get all the nutrients they need and to not negatively impact your fish’s digestive system. Flake food should be used within a few weeks of opening. Feed them regularly, but don’t overfeed them–any uneaten food can rot in the tank and cause bacteria to form in the tank.
  • Do not overcrowd your aquarium. It may be tempting to have an array of colorful fish in your aquarium, but do not overpopulate your fish tank. Overcrowding with too many tank mates can cause a variety of problems, such as low oxygen levels or high levels of ammonia from excretions. If you really want more fish but your current tank is looking crowded, either get a second fish tank or upgrade to a bigger aquarium that will accommodate all of your fish.
  • Prevent aggressive behavior. Overcrowding can also encourage aggressive behavior from some of your fish which results in bullying other fish. Aggressive behavior can also happen when you add a new fish to your aquarium. Always research your fish species before adding new ones to your aquarium to make sure that all of the species are compatible. Transfer aggressive fish to a separate tank.
  • Always quarantine any new fish for a minimum of 2 weeks before introducing them to your aquarium. The tank conditions at pet stores are not always the best, so you want to make sure you did not purchase an infected fish. Monitor them in the quarantine tank during this time for any sign of disease.

Remember, it’s easier to spot a stressed fish than it is to diagnose and treat a sick fish.

Treatments for Dropsy

Treatment is only likely if dropsy is determined early on. Otherwise, the chances of your fish’s survival are slim as there are usually other underlying conditions that accompany dropsy that they must battle, such as popeye. However, if you do detect dropsy early enough, your infected fish does stand a good chance of recovery with some patience and care.

If you suspect that one of your fish has dropsy, quarantine them in a hospital tank immediately. Although the disease is not always contagious, you don’t want to take the chance of infecting the other fish in your aquarium. Change the water in the original fish tank right away and monitor your other fish for symptoms. Keep the temperature of the hospital tank as similar to the fish’s original tank as possible so as to not increase stress in the already infected fish.

Once you quarantine the infected fish, add one teaspoon of salt per gallon of water to their tank to help with the osmotic balance of the fish and get rid of the excess water in their body that causes dropsy. An API aquarium salt is inexpensive and effective. Change the water regularly and add salt each time. 

If your fish is still eating, keep feeding them high-quality foods.

You can use the regular flake or pellet food that your fish usually eats, or you can incorporate live foods and frozen foods into their diet, depending on the species of fish. You can also give your sick fish antibacterial food or mix their food with an antibiotic.

Sometimes, in the early stages of dropsy, feeding your fish is enough to see them make a full recovery.

If your fish is not eating or responding to any other treatment this far, you’ll have to skip directly to treating your fish with an antibiotic. To treat your fish, use a broad-spectrum antibiotic, such as Maracyn-Two. Based on the antibiotic’s instructions, add the required amount to the water of your fish sick’s hospital tank. Maracyn-Two is effective in treating a broad range of bacterial infections and is absorbed by the skin of the fish.

Treat your infected fish over the course of 10 days. If after ten days, you see no improvement in your fish, there may be nothing else you can do, as dropsy is often fatal. Euthanization may be your last option. Consult your veterinarian at this stage. 

Last Comments on Dropsy

As much fun as owning an aquarium can seem, it requires a lot of diligent care to maintain your fish in good health. Aquarium fish are susceptible to a number of diseases, some of which can cause serious damage to your fish, such as dropsy. 

The truth is that dropsy is a condition that is often fatal in fish. Signs of the condition will usually be apparent in your fish’s body, and although there are some treatments available to help your fish recover, there’s no guarantee that it will survive. 

Your best course of action is to prevent dropsy or any other diseases by eliminating any factors in your aquarium that may cause stress in your fish. Keep your tank clean and feed your fish a proper diet of high-quality foods to maintain their immune system and help them fight off any unwanted bacteria. Monitor your healthy fish and note any change of behavior, as that might be early signs of illness. 

If you take good care of your aquarium, your fish are unlikely to get sick. However, as a precaution, make sure that you always have a hospital tank and antibacterial medicine ready in case any of your fish do show signs of illness.

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