6ddd20e8_Common_diseases_of_goldfish__Treatment
[Disease and Causes] Lymphocystis Caused by an iridovirus [Symptoms] The virus causes crusty grey-white lumps to develop on the skin and fins. These may affect freshwater or marine fishes, and sometimes take on the colour of the underlying skin. These lumps are clusters of enlarged cells. [Reason for Infection] The disease is viral, but may be triggered by stress, poor handling or poor water. Some fish may carry the virus without showing symptoms. [Action] The disease rarely kills, although lesions may become secondarily infected. Ideally, infected fish should be isolated. [Treatment] 
There is no known treatment. Some vets recommend the surgical removal of the lesions.
Common diseases of goldfish
Treatment