What is dropsy?

Dropsy: A disease in fish in which the scales stand out from the body and no longer lie flat. The result is usually a pinecone-like appearance to the fish; this may also cause bloating of the body and protrusion of the eyes. In advanced cases, damage to internal organs may occur, leading to organ failure.

Dropsy is almost always fatal if untreated. It is caused by a defect in the kidneys, which are responsible for maintaining electrolyte balance in the fish’s body fluids. The scales become rough and stick out, mainly on the head of the fish, looking like pinecones.   Their eyes also protrude prominently from the head.

There are four stages to dropsy:

·          The fish’s scales become raised and ragged, giving it a pinecone appearance.

·          Bloating of the body occurs as fluids accumulate around the organs and tissues.

·          Gas accumulation in the tissues causes swelling of the abdomen and gives the fish a “pop-eyed” appearance.

·          The scales become rougher and begin to protrude from the body while the eyes appear protruding; fluid accumulation may cause the scales to separate.

The reason for this is not fully understood, but it has been shown that dropsy is always accompanied by bacterial infection and often occurs after a stressful incident such as overcrowding or poor water quality.

What causes goldfish dropsy?

Dropsy is thought to be caused by a diet rich in protein and low in fiber, as well as overcrowding, low oxygen levels and/or poor water quality. The fish’s body is unable to absorb nutrients and proteins due to the buildup of waste products in its blood, and begins to swell as excess fluid accumulates.

There is no known cure for dropsy.  Treatment may prolong life by a few days, but death normally follows within 24 hours after symptoms with swelling and protrusion of the eyes appear.  Dropsy is always fatal if untreated.


Goldfish become infected with dropsy when a bacteria,  ‘Mycobacterium aurum’ infects the fish.  The infection is most commonly spread from another fish that has been carrying the disease for months to years without showing symptoms.

Once mycobacterium aurum invades a goldfish’s blood stream, it can infect other organs in the body.  The most common infection site is the liver. This is why the first symptom of dropsy is often a swollen abdomen.  

Goldfish don’t grow tumors like mammals do, so an infected fish with dropsy may not appear to have a tumor at all. However, tumors can still form and damage the fish’s internal organs.   

The swollen abdomen, which is a result of fluid buildup, will cause scales to stick out and appear as if the goldfish has pine needles stuck in its scales.  Not only does it look uncomfortable, but it may also slow down or stop the fish from eating altogether.          

Dropsy is a bacterial infection that causes fluid buildup in the fish’s tissues, which can be deadly for infected goldfish.      

If the swelling of the abdomen is extreme it may appear as if the fish has swallowed a tennis ball or basketball and look like it’s pregnant (hence, “dropsy”).  The fish may also lie on its side and float as if it is dead.        

Dropsy can be treated but unfortunately, not all goldfish that contract dropsy will survive. If you suspect your goldfish has dropsy, the best course of treatment is to quarantine it in a container where there are no other fish so that it cannot infect other fishes in your aquarium.


If you notice any of the symptoms listed above in your goldfish, it is best to consult with a specialist immediately. There are many remedies that people recommend for dropsy, but the only known effective treatment for this condition is antibiotics and anti-inflammatory medications prescribed by a veterinarian.  Most goldfish that contract dropsy will not survive even if treated with appropriate medication; however, there are some successful cases where goldfish have made complete recoveries when they were quarantined and treated with antibiotics.

There are many home remedies that people recommend to treat dropsy, but the only known effective treatment for this condition, as we mentioned, is antibiotics and anti-inflammatory medications prescribed by a veterinarian.  Some of these antibiotic and anti-inflammatory medications include: Furan Two, Baytril, Zithromax, and Metronidazole (Flagyl).

Goldfish with dropsy should be treated in a separate aquarium.  It is important to do frequent water changes of at least 25% every day while treating the fish with antibiotics and anti-inflammatory medications.  The water change schedule will reduce nitrate levels which can inhibit healing, and will remove harmful toxins produced by the bacteria.

Dropsy reoccurs in some cases because even when the swelling is reduced or goes away, goldfish can remain carriers of the disease without showing any symptoms.  Currently there isn’t a test that can easily identify carrier fish; however, if your goldfish has dropsy it should be considered a carrier.

Carrier fish can spread dropsy to other goldfish, and should be treated with the same medications as your infected fish.  Dropsy is also contagious for koi, so don’t add any additional koi to your pond until they have recovered from their illness and returned to eating a normal diet.  Koi with dropsy will not recover from this bacterial infection.  Dropsy can be effectively treated in koi, but they must also be quarantined from other fish during treatment.

Bacterial Treatment Options

Goldfish normally have an organ called the swim bladder that allows them to control their buoyancy. The epidemic dropsy bacteria damages this organ and causes it to fail, which results in the characteristic bloated belly seen in goldfish with dropsy. When the swim bladder does not function properly, less oxygen is absorbed through the gills; therefore, the fish must actively seek out new sources of oxygen.  This results in increased activity, which can stimulate appetite, but all goldfish with dropsy eventually refuse to eat because their digestive organs are affected by the disease.

You can always lowly raise the water temperature into the low to mid 80s F (27-29oC). This prevents the bacteria multiplying.  Dropsy bacteria are difficult to remove, even with high water temperature though.


Dropsy can be prevented by practicing good pond management and following a few simple steps:  Maintain proper water quality, reduce overcrowding, quarantine new fish for at least one month before introducing them to your pond.  If you plan on buying new goldfish or koi, always quarantine them first.  Don’t overfeed, and don’t allow uneaten fish food to fall to the bottom of your pond where it can pollute the water.

Also make sure you never overcrowd your goldfish or koi in your pond.  The more fish you have in an aquarium or a pond, the higher the chances are that one of them will contract dropsy, because stressed and overcrowded fish are more susceptible to disease.

Goldfish and koi should always be fed a balanced diet.  Don’t overfeed your goldfish; this isn’t healthy for them and can lead to several diseases such as constipation.

Final Thoughts

Dropsy is a very serious bacterial infection that affects your goldfish’s organs while causing it to swell up with fluid. The swollen belly that dropsy causes will prevent the fish from swimming normally, and can even cause them to float upside down because their buoyancy has been affected.

Dropsy is also contagious for other koi if your goldfish has the disease.  If your fish contracts dropsy, immediately quarantine them in a separate aquarium or pond to prevent other fish from getting sick.

Dropsy is extremely contagious for koi, and no matter how hard you try some of them will die if they contract this bacterial infection.  The best way to treat your goldfish is to quarantine the infected fish and medicate them as soon as possible.  Sometimes dropsy reoccurs because some goldfish are carriers of the disease without developing any symptoms themselves, so it’s best to practice good pond management to prevent overcrowding and poor water quality from ever occurring.


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