Hopefully it's not this :
Signs: Fishes so affected often have a swollen belly, and scales may stick out at 90 degree angles from the body, giving the fish the appearance of a pinecone. A red vent and ulceration's may also be present, as may long, pale fecal casts. Fluid may accumulate within the body cavity.
Occurrence: Since dropsy may be caused by one or more factors, it is difficult to point to one common cause.
Treatment: Once the first signs of dropsy are noted, the infected fish should be started on a 14 day regime of antibacterial medicated food. A 24 hour bath in 2 PPM
nitrofurazone is also indicated. If you can bring the fish to a vet, you may wish to administer ceftazidime at 30 mg
/kg IM for three treatments, each two days apart. Since this is a rather expensive treatment, it is usually reserved for larger and more expensive fish. If it is a bacterial problem, this should clear it up. At the same time, an examination of the fishes environment should be made. How is the water quality? Is the diet adequate for this species, and is it being fed a variety of fresh foods? If after 14 days this condition does not reverse itself, you have to consider that the problem is either viral, metabolic, or genetic, none of which are treatable. In some cases, the kidneys of the fish may simply shut down, causing an accumulation of fluids. The best thing to do here is to painlessly euthanize the fish. The best way to do this is to place it into a small container of water, and place that in your freezer. The fish will painlessly "go to sleep" as the temperature drops, and all body processes will stop."