Dropsy Fish Disease: Cause, Symptom, and Treatment


Have you ever seen a picture of a goldfish with a belly so big it’s about to burst? Rotund and likely laying on the bottom, this poor specimen may have had Dropsy. The term Dropsy was originally used in human medicine is less modern times. This was a catch all term that usually meant edema (fluid retention and swelling of tissue) or ascites (fluid retention in the abdomen). In fish, this disease process will ultimately give the animal an overly large belly, damage its buoyancy, and can lead to death. So the name “Dropsy” stuck when it came to describing this malady of fish.

Dropsy Cause

Not contagious in the sense you expect, Dropsy is generally caused by a bacterial infection that lives normally in your tank. Think about how there is bacteria everywhere and every day that rarely infects us until we have a wound or illness. Aeromonas, the most common bacterial cause of Dropsy, is living in your tank already, minding its own business. While this microbe is often the culprit, because Dropsy is a set of symptoms, it can have other etiologies. As with most aquatic diseases, water quality, cleanliness, and minimizing stress is key to prevention.

The most common inciting cause of Dropsy is poor water quality. Poor water quality can weaken their immune system even if a single parameter is overtly affected. New aquarists may encounter this problem if they haven’t given enough time and effort into balancing the nitrogen cycle before adding additional fish. Moderate to severe spikes in ammonia and nitrite could put them at risk for infections, as well as other health problems.

Dramatic changes in water temperature and pH can also cause a strain. Further points of stress could be aggression between individuals or poor nutrition. Under feeding, as well as over feeding, can also make your fish sick. Common species affected are those that produce high ammonia waste and may live in smaller tanks, such as goldfish or betta fish. Once identified, your fish may only have 1-2 weeks to live, so it’s best to act fast when the first signs appear.

Fish with Dropsy Disease
Fish with Dropsy Disease

Dropsy Symptoms

Aside from the tell-tale sign of a bloating abdomen, there are other subtle signs you should look out for. Many of them are considered general signs of illness, but even early changes in your pet’s behavior or appearance should be investigated. Below we’ve listed several clinical signs you may notice, in no particular order.

  • Poor appetite
  • Excessive slime coat
  • Pale, stringy feces
  • Hiding or other changes in behavior
  • Fins clamped against abdomen
  • Pale gills or loss of color

Along with abdominal dissension, you may find the animals’ eyes bulging or their scales lifting up. These are all directly due to the fluid retention. One other disease process that can appear similar to Dropsy is Gas Bubble Disease. If the water becomes over saturated with oxygen, air can build up inside the eyes or abdominal cavity of fish. With hyper saturation you generally will see air bubbles inside the eye instead of it just being enlarged.

Egg binding is another red herring.  Female fish that are egg bound and undergo dystocia may appear abdominally distended. This should not be confused with normal pregnancy though. Heavy with eggs, her abdomen may be noticeably rounder, but overall her behavior will not have changed. One exception is during breeding season when females may exhibit nesting behaviors, be more territorial, or may even have heightened coloration. Their scales do not be lift up in this condition. If you are unsure of what may be affecting your fish, it’s best to involve your local aquatic health professional.

As the fluid invades the abdomen and other tissues, the fish’s body is literally stretched to it’s limit, causing pain and other complications. In most cases the animal will have trouble maintaining its place in the water column and often will rest on the bottom. Being unable to stay afloat will inevitably lead to trauma and the disruption of their vital slime coat. With an already compromised immune system, this and any other further illness could quickly lead to their demise.

How to Prevent Dropsy

As we’ve already mentioned, maintaining good water quality is the most important thing you can do to prevent Dropsy and many other illnesses from presenting. Regular removal of waste, routine partial water changes, and maintaining a clean filtration system are very valuable to the health of your tank. Tank overcrowding and evidence of aggression should be addressed right away as well. Proper nutrition and adequate food amounts are also helpful.

Dropsy Treatment

Even though it is not “contagious”, when it occurs you know there is good evidence that something is wrong in your tank and other fish may be affected. Isolate the sick individual(s) in a hospital tank first to ensure they have a stable water quality while you address the problems in your main tank. This will give their immune system a break and a little time to try and recover. Initial action should be taken within 24 hours of the first signs of Dropsy if you want to improve your odds of success.

Some aquatic professionals may argue that euthanasia is the best option because it can progress quickly and create compounding problems. There’s never any guarantee that treatment or environmental improvements will cure your animal. Considering the potential seriousness of this illness, it may be best to consult an aquatic veterinarian, but we will briefly discuss treatment below. 

Now that your sick individual is in its hospital tank you can consider treating. High grade, high percentage Epsom salts is a consideration for this. You want to avoid formulations with other ingredients or oils as this may harm your fish or upset your water quality. The magnesium in the salt can help draw out the excess fluid. This is also commonly used for constipation in fish and in humans because of this. Dosages seem to vary on hobbyist forums, but 1/8 of a teaspoon per five gallons is a conservative dose frequently discussed.

 Broad spectrum antibiotics should never be used on your primary tank without the guidance of an aquatic health professional. These treatments can kill not only the bad bacteria affecting your fish, but the good and essential ones keeping your nitrogen cycle balanced and alive. Decimating these vital microbes will cause heavy spikes in ammonia and nitrite that could ultimately lead to a full tank die off.

Treatment in the hospital tank exclusively avoids this issue for your show tank. Antibiotics that are broad spectrum and target gram negative bacteria are commonly used for these infections. A popular brand, Maracyn-Two, consists of the antibiotic minocycline. This is used for 5-10 days depending on the severity. It also may be useful for fin rot, if present. In some cases antibiotic impregnated feed may be more appropriate, but this is best determined by a veterinarian.

Melafix is another familiar product that is made from Cajeput Oil. It is thought to have some antiseptic properties and is used often with infections. Dosing instructions indicate using 5 mL to every 10 gallons. It may cause a little foam at the top of the water and have a fragrant smell. Treatment may need needed for several days.

Dropsy and Species Specific Consideration

High waste producers such as goldfish, guppies, and koi are more prone to degradation of water quality and will need more frequent monitoring. Fish that are commonly kept in smaller tanks such as Betta fish, neon tetras, and guppies are more likely to have dramatic shifts in water quality over large systems just because there’s less water to dilute the problem. Outdoor koi ponds should be assessed for contamination with parasites, chemicals, and any other possible peril from being out in the open.

Dwarf Gouramis may exhibit this symptom when infected with the Dwarf Gourami Iridovirus.

When affected, frogs can bloat up so much they look like they want to float away. As with fish, there can be many causes, some of which are poorly understood. Proper husbandry may be even more important in amphibious species because of their additional needs. Humidity and lighting variables may also play a part. If a bacterial infection is suspected, it’s possible you may even need to sterilize the tank and start over.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

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