Dropsy In Fish: Causes, Symptoms & Treatment (2024 Guide)

An Aquarium Full of Fish
An Aquarium Full of Fish
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: July 10, 2024
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Most people who keep freshwater aquariums will probably come across dropsy, a common affliction. Misdiagnoses frequently turn this condition lethal in many instances. Drawing on our expertise, we’ve put together an in-depth guide to correctly identify dropsy and a detailed treatment plan to aid you and your aquatic friends.

Article Summary

  • Dropsy, which is caused by a bacterial infection, is a common disease in freshwater aquarium fish, resulting in the buildup of fluid in the fish’s body cavity and tissues.
  • Preventing dropsy involves maintaining good tank-keeping practices, such as providing a healthy diet, avoiding overfeeding, ensuring proper water quality, and maintaining the right water temperature.
  • Treatment methods include quarantine, Epsom salt baths, and antibiotics in severe cases.

What is dropsy in fish?

Dropsy is the buildup of fluid inside the body cavity and/or tissues of sick fish and is caused by a bacterial infection. Dropsy can indicate a more severe, underlying condition and is often confused for swim bladder disease or constipation.

Generally affecting freshwater fish, the dropsy fish disease can give a healthy fish a severe infection and even prove fatal in as little as one day.

Here’s a short video explaining dropsy in fish.

Fish Facts – “Dropsy” in Freshwater Fish

Dropsy vs Swim Bladder Disease

Since dropsy can be caused by any infection of the swim bladder, tumors, intestinal blockage or bacterial infections, dropsy is generally considered to be more of a symptom than a disease.

Many people mistake swim bladder disease for dropsy. It is important to note that where swim bladder disease is caused by internal gas buildup, dropsy is caused by internal fluid pressure in the body cavity and tissues.

Goldfish With Swim Bladder Disease
(1) Goldfish With Swim Bladder Disease

Swim bladder disease can be due to physical abnormalities, environmental, mechanical, or genetic issues whereas dropsy is an infection brought on by a weakening immune system due to environmental factors.

The easiest way to differentiate between dropsy and swim bladder disease is the bloated scale position. If the scales are straight out, or pine cone like appearance, your pet fish has dropsy.

Is dropsy contagious?

While the dropsy fish itself is not contagious if one of your fish catches it, more will follow. This is because dropsy is caused by a bacteria that is naturally occurring in aquariums. Poor water quality causes your fish’s immune system to weaken allowing the infection to take hold.

If you are housing multiple fish in one aquarium it is likely that all of their immune systems will be weakened and they will become susceptible to the disease.

Does dropsy kill fish?

Yes, dropsy is fatal, even with proper treatment. Dropsy is a fast acting disease and even experienced aquarists that identify and begin treatment immediately often lose the fish.

How long does dropsy take to kill a fish 

After symptoms begin dropsy becomes fatal 1-3 days later. This fast acting bacterial infection often is misidentified and improperly treated due to similar symptoms in other diseases. Correct identification and treatment often happens too late.

What causes dropsy in fish 

Dropsy fish is caused by an infection by naturally occurring bacteria. This bacteria called aeromonas is present in most aquariums and is generally non harmful. The issue comes when water parameters begin to degrade, allowing the bacteria to multiply. Eventually bacterial colonies reach huge quantities, mixed with the already weakening immune system of aquarium fish due to bad water quality and an infection is bound to happen.

Symptoms of dropsy

Goldfish with Dropsy Disease
(2) Goldfish with Dropsy Disease

Affected fish can have one or more of these symptoms. Physical symptoms such as curvature of the spine, pale feces, swelling, stuck out fish’s scales or protruding scales, liver dysfunction and classic swollen belly are all signs of concern when it comes to dropsy.

Paleness of gills-excess swelling causes gills to distend and appear pale

Pale feces-Fish with dropsy often experience a loss of appetite meaning they will not have normal bowel movements. Instead of seeing normal feces you will only see the stringy, white mucus.

Spinal curve developing-As the abdomen fills with fluid internal organs are pushed aside and will sometimes cause the spine to curve.

Skin lesions-at the same time as your fish with dropsy begins to experience swelling you might see it display skin lesions.

Lethargy-If you notice the infected fish lying flush on the bottom of your aquarium along with some of these other symptoms it may be due to weakness from the disease.

Swollen anus-Excess fluid may build up in the intestines causing swelling that can be seen in the dropsy fish anus.

Abdominal swelling-affected fish will experience a rapidly swollen belly caused by fluid accumulation and internal organs swelling.

Bulging eyes-due to the swelling pressure dropsy fish often experience something called “pop eye” which is where the eye bulges due to fluid buildup

Scales falling out-some severe cases can make your fish begin to lose their scales.

Dropsy vs Constipation

Because one of the main symptoms of dropsy is bloatedness it is often mistaken for constipation. There are a few ways to differentiate the two;

  1. Is your fish excreting regularly?
  2. Are the water parameters good?
  3. Are the scales sticking straight out?

If you answered no to 1 or 2 there are some other possible diseases such as swim bladder infections or parasites. If you answered yes to #3 It is very likely that your fish has dropsy.

Can a fish recover from dropsy? 

Dropsy fish is one of the hardest diseases to cure, but if caught in the early stages there are treatments that you can try.

For very mild cases weekly partial water changes and a fresh, high quality diet can be enough to start disease recovery.

How to cure dropsy in fish

A quarantined goldfish
A Quarantined Goldfish

When dealing with dropsy fish disease it is important to know that there are a few tried and true treatment methods. While not all aquarium fish will respond to dropsy treatment it does give them a fighting chance.


As soon as you identify that one of your fish has dropsy you should immediately move them to a quarantine tank. While dropsy isn’t contagious, placing a fish in an isolated fish tank will allow you to perform treatments without stressing out other aquarium fish.

Epsom Salt

Stop feeding the sick fish 24-48 hours before performing a salt bath. For a salt bath you will need 3 tanks: the treatment or hospital tank, the revival tank, and your quarantine fish tank.


Aquarium salt and epsom salts are two different things. Aquarium salt is designed for use in freshwater aquariums, but epsom salts can increase the hardness and adjust pH levels in a fish tank. We recommend epsom salts here but it might be more appropriate to add aquarium salt in other cases.

To the treatment tank: add 1 teaspoon salt for every 1 gallon of water. 

To revival tank: mix 1/4 treated salt bath to 3/4 aquarium water 

Quarantine fish tank: do not place any salt into this tank 

To prepare the salt bath add salts to warm water (1 tsp for every 1 gallon water) let dissolve and add to respective treatment or revival tanks. Allow water to cool to room temperature. 

For the salt bath: place the fish in the treatment tank for at least 5 minutes but no longer than 8 minutes. Watch for rapid breathing or any signs of struggle, if displayed move to the revival tank immediately.


You might be wondering why we use salt in a freshwater aquarium to treat fish disease. This is because adding salt to an aquarium the aquarium fish’s kidneys don’t have to do as much work because the fish’s blood salinity and the water salinity is equal. However, freshwater fish cannot exist in this state for long periods of time or else it will upset their osmotic balance.

After 5-8 minutes in the treatment tank move the fish to the revival tank. The purpose is to give some adaptation time in between the salty treatment tank and the freshwater aquarium.

Does Epsom salt help dropsy?

The theory behind using epsom salts is that it will help drain fluid out of your fish’s tissues and reduce swelling. Much like tired athletes use epsom salt baths to reduce swelling and relax, your sick fish will experience the same soothing effects.


In more severe cases treating dropsy can be exacerbated by using antibiotics. Any broad spectrum antibiotic for gram-negative bacteria should help treat dropsy disease. A popular one is Melafix, which includes a botanical tea tree extract to help heal any open wounds and restore the natural slime coat.

Can you drain dropsy?

It is generally thought since dropsy is caused by a buildup of fluid that you are able to drain it with a syringe. However this fluid isn’t sitting somewhere easily drainable, instead it is within your fish’s soft tissues. Therefore, it is impossible for you to drain the fluid

How to prevent dropsy

Dropsy disease is most often caused by bad tank keeping practices. Like many tropical fish diseases, dropsy disease is an internal bacterial infection that affects fish that are experiencing many stress factors.


Fish Food
Fish Food

To ensure your fish’s best health you should feed them a high-quality healthy diet appropriate to their breed. Be sure to feed your fish a varied diet, and ensure that all tank mates in your community tank are getting enough food.


New fish keepers often overfeed their aquarium fish, leading to constipation and bloating which are often mistaken for dropsy fish disease. Overfeeding can also lead to uneaten fish food being left in the aquarium to foul the tank water. 

Water Quality

Poor water quality is probably the most common cause of fish disease. Remember, dropsy refers to an infection due to a bacteria that is naturally in aquariums, infected fish just have weak immune systems and are not able to fend off the bacteria.

Keeping your tank clean ensures that many fish diseases, not just dropsy fish disease does not affect one or more fish. Ensure your fish tank is always clean, and if you notice that your tank is turning cloudy or dirty, immediately address it to avoid diseases and keep your fish healthy.


Water temperature is also a common cause of dropsy fish disease as having an improperly heated or cooled tank will cause unnecessary stress on your fish’s body. Aquarium fish are very sensitive to water changes and water outside of their temperature range can shock their body, making them susceptible to diseases. 

How To Clean Tank After Dropsy

After moving one fish to the quarantine tank to treat dropsy you should clean the community aquarium to ensure that other fish do not get sick. While it is likely that your other fish already have a weakened immune system and are susceptible to dropsy cleaning your tank can help prevent a severe case.

Generally with diseased fish I like to completely start over with the tank and clean with a 50/50 solution of vinegar and water, being sure to thoroughly scrub all decor, plants, and the filter with the solution.

Man Changing Water in Aquarium Using Siphon
Man Changing Water in Aquarium Using Siphon

However, for larger fish tanks, and ones where you can’t take all of the organisms out this is impractical. In these cases we recommend using a potassium permanganate solution to dip decor and plants (not the roots!) and thoroughly rinse before returning to the tank along with a 50-70% water change.

Remember, dropsy is caused by naturally occurring bacteria in your aquarium so you’re not getting rid of the bacteria, instead you are ensuring that any bad water parameters are no longer present to continually weaken your fish’s immune system.


When cleaning the tank after dropsy I would go so far as to net my fish back into the original tank to make sure no excess water get’s back in.


In conclusion, dropsy is a condition that strikes fear into every fish owner’s heart. It is something every aquarist has to deal with eventually, and has proved fatal for many fish. The lesson to be learned is that you should keep a close eye on your aquarium fish to catch signs and begin treatment as soon as possible.

(1) Humanfeather / Michelle Jo, CC BY 3.0, via Wikimedia Commons
(2) Taipan198 at the English-language Wikipedia, CC BY-SA 3.0, via Wikimedia Commons

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