There are few major kidney and urinary tract disorders seen in fishes. Of these the main kidney and urinary tract disorders are Renal Dropsy, Carp-dropsy complex, and Proliferative kidney disease (PKD).
1. Renal dropsy in fishes is caused by the parasite, Sphaerospora auratus. Renal dropsy usually occurs in pond-raised goldfish. There is damage to the kidneys and swelling of the abdomen due to fluid accumulation is the most common sign of renal dropsy. There is no treatment for this kidney disorder and it usually causes death of the infected fish.
2. Carp-dropsy complex is a kidney disorder that usually affects the carp and goldfish. The Carp-dropsy complex disease is caused by the parasite, Sphaerospora angulata. Other complications include viral and bacertial infections, and carp swim-bladder disease. This is why this kidney disorder is called Carp-dropsy complex.
Similar to Renal dropsy, there is renal damage, along with an enlargement of the fish's eye (exophthalmos). The treatment is usually unsuccessful and death occurs within six months.
3. Proliferative kidney disease is caused by the PKD parasite, and has become the most important kidney and urinary tract disorder to affect the fish industry. It usually occurs in rainbow trout and other fishes belonging to the salmon family. Proliferative kidney disease infects young fish, generally during summers when the temperatures rise above 12 degrees Celsius.
Fish with the disease will display sluggishness, bulging of the eye (exophthalmos), renal dropsy, accumulation of fluids in the abdomen, and swelling of the lateral side of the body. Unfortunately, treatment for Proliferative kidney disease is not usually successful.