Lymphocystis is a common chronic disease of several of the higher order of salt and freshwater fishes. Characteristic benign papilloma-like lesions usually develop on the surface and may occur on the internal organs and tissues in rare cases. The disease can be transmitted experimentally by exposure to water containing virus, and by feeding or injection of infected cell culture fluid. Lymphocystis disease (LD) and its causative virus, fish lymphocystis disease virus (FLDV) occurs world-wide and the rate of incidence seems to be increasing.