The bacteria which cause this disease commonly are in each type reservoirs – in aquarium also. These bacteria normally aren't harmful to fish. So why the fish are sick? They are sick because their immunity rapid decreased by wrong diet (monotony diet without vitamins and microelements or indigestible diet), rapid changes of water parameters (especially wrong water temperature), bad water quality (faulty nitrogen cycle – accumulation of ammonia or nitrites, accumulation chlorine, chloroamines, oxygen-poor water), too much fish, stress. The bacteria attack internal organs of the fish: the liver, intestines etc. which reduce. Damaged kidneys doesn't filter blood so the fluids accumulate in the body. The disease causes inflammatory reaction of the body and it progress leads to death.
We must find primary cause of this disease because the bacteria attack only weak fish with poor immunity. We don't have any evidences that this disease is contagious unless it is secondary infection. In other words fish suffer from dropsy because they earlier became ill from other illness e.g.: parasitic or viral disease. We should commit an act euthanasia fish when we note an exudate with them.