Notice the protruding scales on this goldfish with dropsy.
Symptoms and Causes
The symptoms of dropsy in fish is a distended or swollen body with protruding scales. Dropsy is also known as ascites. The affected fish may appear lethargic and may not eat.
Dropsy isn't a disease itself, but actually a symptom of another underlying disease in the fish.
The reason the fish's body swells is due to a build up of fluid in its body cavity and internal organs. This may occur if the fish's kidneys are affected, for example. There can be many different causes of fish dropsy, and it is usually difficult to know exactly what the cause is.
However, one common cause of dropsy in fish is a bacterial infection by Aeromonas. Aeromonas is normally present in all aquarium water, however, it sometimes causes illness in fish, especially fish that are stressed due to poor water quality from overcrowding or infrequent partial water changes. Also, some species of Aeromonas are more pathogenic than others. Infection by Aeromonas will sometimes cause red streaks or sores on the fish's body (but not always).
Treatment for Fish Dropsy
If you have a fish with a swollen, distended body typical of dropsy, it is best to isolate the fish and treat it in its own treatment tank if possible.
You can treat the fish by adding a small amount of epsom salts to the tank. Epsom salts consist of magnesium sulfate as opposed to sodium chloride found in regular aquarium salt (and table salt). Adding epsom salts to your tank will help to draw some of the excess water out of the fish's body cavity and tissues. Don't add more than 2.5 teaspoons of epsom salts per 10 gallons of water.
You should feed the affected fish antibacterial fish food for 7-10 days if the fish is still eating. You can also add some Maracyn Two to the aquarium that the fish with dropsy is in. Maracyn Two treats gram negative bacterial infections, such as Aeromonas, and is absorbed through the fish's skin from the water.
However, unless you start the treatment early the fish may still not survive. It is also possible that the dropsy may be caused by something other than a bacterial infection, such as a virus, or some other cause. If this is the case then the antibiotics will not be effective.
You can often prevent bacterial and other diseases in your fish by doing regular partial water changes (20-25 %) in your tank each week. In fact, if you have the time, doing partial water changes twice a week is even better. And of course, don't overcrowd your fish or overfeed them.