What Causes Dropsy In Fish: Symptoms & Prevention | Aquascape Addiction

What Causes Dropsy In Fish: Symptoms & Prevention

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This is a detailed guide that looks at what dropsy is, what causes it, symptoms and most importantly how to treat it the right way. Many fish can be effected by dropsy and it's very important to diagnose early for best chances of both treatment and prevention.

What Causes Dropsy In Fish: Symptoms & Prevention

You may have already heard of a disease called dropsy. Yes, it is a disease that affects humans, but of course today we are here to talk about dropsy in fish.

What causes dropsy in fish is the main question we want to answer today. However, there are many other things to know about this deadly disease such as what it is, causes, symptoms and most importantly how to treat it so let’s get right to it.

What Is Dropsy?

Ok, so to be perfectly clear, dropsy is actually a bacterial infection in your fish. Technically speaking, dropsy is the buildup of fluids in the tissues and body cavities of fish, usually in the abdomen.

The bacteria which cause dropsy in fish are present in pretty much every aquarium out there. The point here is that all fish can catch dropsy if the conditions are right, or should we say if the conditions are wrong.

Since all fish are exposed to the dropsy causing bacteria, it is usually only the fish which are already sick or weakened which will contract the disease. It is definitely possible for a tank wide outbreak of dropsy to happen if all of the fish in your tank are stressed out.

What is also true is that dropsy is often the effect of other diseases. Fish who contract dropsy may very well already be suffering from a wide variety of other conditions, all of which make them susceptible to the bacteria.

If your fish are already sick, it makes it much more likely for them to contract dropsy due to a weakened immune system. What you need to know about dropsy is that it does have a fairly high mortality rate. Even when it is caught early, it is still often fatal. Often it is caught way too late for any kind of treatment to be effective.

This is because by the time you notice that your fish has dropsy, whatever caused your fish to become stressed and unhealthy may already be past the stage where any kind of treatment is effective. In the end, it is either the underlying cause of the dropsy or the dropsy itself which will spell the end of your beautiful fish.

The Causes Of Dropsy In Fish

Like we already mentioned before, dropsy is caused by a special kind of bacteria that is present in pretty much every aquarium out there. However, only the fish that are already sick, stressed out, and have a weak immune system are susceptible to the bacteria which cause it.

Therefore, it makes sense to know what kind of factors can weaken a fish enough to become susceptible to dropsy. So, what causes dropsy?

  • Poor water quality can definitely be a cause of dropsy. If your fish live in dirty water that is full of bacteria, chemicals, toxins, and unwanted substances, it can wreak havoc on its immune system. You need to make sure to have a good filtration system that can handle the bio load in your aquarium. Dirty water makes fish weak, which makes them susceptible to dropsy.

  • Another cause of your fish becoming susceptible to dropsy is a spike in ammonia and nitrate levels. Both of these substances are very harmful to fish, and too much of either of them in the water can kill your fish on their own. However, if the ammonia or nitrates don’t kill your fish, the resulting dropsy infection very well can (we have covered a separate article on lowering ammonia levels which you can find here).

  • A very large and acute drop in water temperature can really mess with the immune system of any fish. The weakened immune system is then not strong enough to fight off the dropsy causing bacteria.

  • An improper diet and bad feeding habits overall can also cause dropsy to occur. If you don’t feed your fish enough, or too much, plus the wrong diet, it will weaken their immune systems and make them susceptible to the dropsy bacteria.

  • Stress is also a big factor. If you have just transported your fish and did not take the time to properly acclimate them to their new home, they can become stressed, weakened, and susceptible to this bacterial disease. There are many factors which can stress fish out, so this is essential to pay attention to.

  • Aggressive tank mates can also cause dropsy to occur. They can hurt and damage your fish, scratching them and exposing them to bacteria. Not only do mean tank mates stress other fish out, but the physical damage they cause can allow the bacteria direct access to the blood stream.

  • There are many other diseases which can leave your fish vulnerable to contracting dropsy. Things like fin rot, rail rot, cotton mouth, a swim bladder problem, and countless other diseases all have the ability to weaken your fish’s immune system to the point where it becomes very susceptible to contracting dropsy.

Fish That Are Susceptible To Dropsy

Some fish are more susceptible to contracting dropsy than other fish. Keep in mind that freshwater fish are usually more susceptible to dropsy bacteria. This is because saltwater tanks usually do a better job at killing of viruses and bacteria.

Remember folks, salt does have its benefits. So, which fish are the most susceptible to contracting this often fatal condition?

  • Betta Fish.
  • Guppies.
  • Goldfish.
  • Danios.
  • Koi Fish.
  • Black Mollies.
  • Cichlids.
  • Angelfish.
  • Arowana.
  • Gourami.
  • Clown fish.

Symptoms Of Dropsy

Dropsy is not something that happens from one day to another. You will definitely be able to see the symptoms of dropsy in your fish. The problem here is that many of the symptoms are the same for various other diseases out there.

However, if your fish is suffering from the majority of the following symptoms, chances are that it has dropsy.

  • An extremely swollen belly and abdomen.
  • The pine-coning of scales (scales stick out).
  • Pale coloration – especially around the gills.
  • Bulging eyes.
  • Pale and very stringy feces.
  • Red and swollen anus.
  • Curvature of the spine.
  • Ulcers along the body.
  • Clamped fins.
  • A lack of appetite.
  • Lethargy and sluggishness.
  • Hanging out near the surface of the water.

These symptoms will progressively become worse and worse, with the color changes, lethargy, and a lack of appetite coming first. Other symptoms like pale feces, clamped fins, ulcers, and other symptoms will come later. The problem is that by the time the deciding symptom, the swollen belly is really visible, it is often already too late.

How To Treat Dropsy

It is definitely possible to save the lives of your fish if you detect the dropsy early enough, but it is no easy feat. The reason why dropsy is fatal in many cases is because by the time detection has happened, it has usually progressed too far to be treatable.

However, you can always try, as you should. Let’s talk about some of the best treatment options for dropsy in your fish.

  • Perform a water change in the tank. You should change at least 30% of the water in order to get rid of as many dropsy causing bacteria as you can. This will also help rid the tank of other toxins and substances which could be making you fish susceptible to dropsy.

  • Clean the filter and replace the media. If your filter is not in prime working order and it is not doing its job, it means that the aquarium water has too much waste, ammonia, and other substances in it. While this is not a direct treatment, it certainly does not hurt.

  • You need to move the affected fish into a hospital tank, so to speak. You need to quarantine the affected fish immediately to stop it from stressing out your other fish and causing them to become susceptible to dropsy as well. Like we said, it is easy for a community wide dropsy outbreak to occur once a single member of the tank is suffering from it.

  • There are special antibiotics which can help to kill off the bacteria while also boosting the immune system of your fish. These antibiotics need to be administered as soon as possible in order for the best fighting chance at survival. A ten day course of broad spectrum antibiotics specially designed to fight this bacteria will usually do the trick if the dropsy is detected early enough.

  • If the dropsy infection is not very advanced, feeding your fish a proper diet of high quality foods can also be enough to treat it. Dropsy is often caused by imporper feeding, so this can definitely help.

How To Prevent Dropsy

There are a few different things that you can do to stop your fish from contracting dropsy. Like we said before, these bacteria are usually always present in every aquarium, but taking the right steps can help prevent them from affecting your fish.

Regular Water Changes

You want to perform regular water changes. You should change around 25% to 30% of the water every 2 weeks. This will help get rid of a buildup of bacteria, waste, toxic substances, and other unwanted compounds, thus helping your fish’s immune system stay in working order. This also helps get rid of some of the dropsy causing bacteria.

A Good Filter

You need to make sure that you have a good 3 stage filtration system in place. Keeping the water clean and crystal clear will go a long way in preventing dropsy. The filter you have should be able to handle around 4 times as much water per hour as the total water volume in the tank.

It also needs to engage in all 3 major types of water filtration for the best results. Also, don’t forget to clean your filter on a regular basis and replace media when necessary.

Regular Tank Cleaning

Clean the tank on a regular basis. This means cleaning the glass, plants, ornaments, and the substrate. This is best done when you do water changes. Using a light bleach solution (25 parts water to 1 part bleach) on rocks, wood, decorations, and plants will help kill off bacteria.

Just remember to rinse the items after washing with a bleach solution because bleach is just as deadly to fish as anything else (we have covered a detailed cleaning guide here).

Don’t Overpopulate Your Tank

Don’t put too many fish in the same tank, or at least do not overcrowd it. If your fish are living on top of each other in a way too close proximity, it can stress them out, it makes them compete for food, and it results in a filter that needs to work overtime to keep up due to a high rate of waste production. These are all things that can make your fish susceptible to dropsy.

A Good Diet

Make sure to feed your fish a good diet. Feed them enough so they are not hungry anymore, but don’t overfeed them either. Also, make sure that you are meeting the exact dietary needs of the specific fish in question. This will help ensure that they have a strong immune system capable of fighting the dropsy causing bacteria.


As long as you provide your fish with a good diet and a good home, dropsy really should not be much of an issue. However, once dropsy takes hold, you need to recognize the symptoms real fast and start treating the causes as soon as possible. Dropsy has a high mortality rate, so the earlier it is detected and treated, the better the chances of survival are.