Dropsy – How to Avoid it and How to Treat it

Dropsy is a rare but serious disease caused by an internal bacterial infection in a fish. The disease can affect many different species of both pond and aquarium fish and is often fatal. If it is caught early, and appropriate measures are taken, it is not uncommon for a fish to fully recover from dropsy. However, if the fish reaches advanced dropsy, it is a death sentence in almost all cases.


The term ‘dropsy’ refers to a fluid build-up inside the body of a fish. If a koi has advanced dropsy, it is very noticeable and recognisable as the fluid inside the koi’s body will cause it to swell and bloat. As the body swells more and more, the scales will develop gaps between them which will make them lift away from the body of the koi. This often makes a koi look like a pinecone and gives dropsy its nickname – ‘pinecone disease’. As well as this swelling, the most frequently seen symptoms of dropsy include bulging eyes, loss of buoyancy, dull colour and/or pattern and a tendency to hide and act shy.



One of the most common causes of dropsy is poor water quality which leads to an environment where fish are in poor health and bacteria can thrive. When a fish lives in such an environment, they often end up having a weakened immune system that leads to bacteria being able to infect the koi when it is ill or injured. This means that poor water conditions do not necessarily cause dropsy, but they do lead to a living environment for the koi where they are much more likely to end up with the disease.

Injuries, such as from herons, often cause nasty infections.

Poor water quality is linked very closely with the next most likely cause of dropsy which is an infected injury. As experienced koi keepers know, it is very important to prevent predators from being able to access your fish. Unfortunately, sometimes they still slip through and cause injuries to your koi. If you already have poor water conditions and a koi is injured, then the injury is very likely to become infected. Even if you have perfect water conditions, if the injury has led to the koi bleeding, the quality of the water is very likely to become poorer. Both of these circumstances lead to a perfect environment for a koi to be affected by dropsy.


It is often believed that dropsy is a contagious disease, but this is not necessarily the case. It is often true that once one fish in a pond has dropsy, other fish in the pond will follow but this occurs because the other fish have been exposed to the same water conditions as the first. Nevertheless, it is always imperative that you have a hospital/quarantine pond available so that as soon as a fish shows the first signs of dropsy, it is removed, and the original pond investigated before the fish is given treatment.


A hospital/quarantine pond does not need to be anything fancy – it can even be a completely temporary set up that can be put away when not in use, such as a stock tank. When you buy new fish there is always a possibility that the fish may have or carry some disease and you need to ensure that this disease doesn’t immediately spread to all of your other koi. To prevent this, all new koi should be quarantined and observed for 14 days so you can ensure it is not showing any signs of illness.


5 in 1 Water Test Kit (NO3, NO2, pH, KH & GH)

In order to investigate the cause of dropsy in a koi, you should test your water to see if you have any obvious issues. Your water should be tested regularly but it is essential to test it when you have any concerns, such as a koi with dropsy symptoms.



If you see no issues with your water conditions and the koi in question has no obvious wounds from predators, there are only 2 more causes possible. These are a lack of proper nutrition and parasites. It is always important to feed your koi a highly nutritious food with high proportions of proteins, fat, vitamins, and minerals to ensure that they have a properly balanced diet to grow and maintain a good body shape. If your koi is not being fed such a good food, their immune system can be compromised and again, they can be vulnerable to dropsy-causing bacteria. If you are confident that you are feeding your koi appropriate food, then the only cause left that is possible is a parasite. Parasites, such as flukes, can damage your koi from the inside and leave wounds inside the body which are impossible to see but lead to the perfect breeding ground for bacteria.



Once you have established the most likely cause for your fish to be experiencing dropsy, the next step is to treat the cause while the affected koi stays in the quarantine pond. If you have poor water conditions, do a water change or investigate how to improve your water. If your koi are not being fed the nutritious food they require, start feeding them appropriate food. If the fish has obvious wounds from a predator but is still acting normally and eating as usual, the best thing you can do is just leave the fish alone. Continue to feed it and check the water conditions but do not handle the fish and stress it and do not apply medications and most wounds will clear by themselves in good water conditions.

Dropsy and Ulcer Treatment

If the wound continues to worsen or the fish is not eating, a medication may be required. Consult a vet or a professional in this instance.



If treating the cause is not helping the fish after a few days to a week, or the most likely cause is parasites, you need to consider using a dropsy medication on the koi. Most dropsy medications are very harsh and so should not be used unless necessary and should only be used on the affected fish in a suitable quarantine pond.



Advanced dropsy is difficult to treat and, usually, the koi will not be able to recover, but if you notice the symptoms of dropsy quickly and take suitable action, it is likely that your koi will make a full recovery from dropsy and will be able to be released back into its normal pond in no time at all!


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