Dropsy is not a disease diagnosis, but is actually a descriptive term for the clinical signs observed in fish. The causes are not limited to bacterial and viral infections, but it can occur as a result of skin disease, gill disease, renal disease or congestive heart failure which can have a variety of aetiologies.
The term has often been misused as being diagnostic for bacterial disease, when all it actually means is an abnormal accumulation of fluid in a body cavity or in the subcutaneous tissues. Another medical term that can be used is anasarca.
Clinically, the scales of the fish will protrude from the body (due to subcutaneous oedema), giving them the classic “pine cone” appearance. Fluid may also accumulate in the coelomic cavity, giving them a “pot-belly” appearance. This condition is limited to fishes in a freshwater environment and the reason for this is explained in the following sentence. Fishes that live in freshwater are in a hypo-osmotic environment. And so, if there are any severe external lesions (e.g. large skin ulcers from bacterial infection or severe gill damage from fungal infections), there could be a net influx of fluid into the body. If the kidneys are damaged such that normal excretion of urine is reduced, dropsy can also result.
Prognosis is poor and such fish should be euthanased. It is useful to examine the diseased fish immediately post-euthanasia to identify the reason for the disease to prevent it from occurring in its tankmates.
- Essani K, Granoff A (1989) Amphibian and piscine iridoviruses proposal for nomenclature and taxonomy based on molecular and biological properties. Intervirology 30(4):187-93