Dropsy is an extremely common condition that afflicts pond fish. Not considered a disease, dropsy generally results from another cause such as a parasite that triggers a bacterial infection. It is vital to catch dropsy early on in your fish because it is almost impossible to cure in the final stages.
Signs of dropsy include reddening at the base of the gills, ulcers and paler gills. In the infection's end stages, the fish will bloat from its head to tail. The kidneys no longer function so the excess fluid has nowhere else to go. (This bloating is best seen by viewing the fish from the top.) Sometimes the eyes will even pop. In severe instances, the scales will stand out, giving the fish a pine-cone like appearance.
Dropsy is not thought to be contagious from fish to fish, but the conditions that cause dropsy may be. So it important to find out if poor water quality, overcrowding, improper handling of the fish or poor nutrition may be the root cause.
Once you've identified fish with dropsy, you should immediately remove the infected fish, and if the pond's fish are generally sick change approximately 50 percent of the water and keep the fish stock low.
Prevention is key to limiting dropsy in your pond. In the fall, skim the pond for debris because parasites and bacteria will feast on the leaves and other organic materials throughout the winter. Skimming also makes for easier springtime cleaning which is instrumental in keeping parasites at bay. If your pond is small (under 3,000 gallons), drain the pond completely, clean thoroughly, and collect the debris with a wet vac.
For more "high-tech" ponds that use bottom drains and UV lights you should prepare a salt treatment and clean the system while inspecting your fish for any stress.
Many experts recommend that you destroy fish in the final stages of dropsy. If you believe that you've identified it in the early stages, you can remove the fish from the pond to a tank with a higher water temperature, add Epsom salts or apply a course of antibiotics.
Before using antibiotics on your fish, check with a veterinarian or a fish expert to determine the right drug and dosage.