Lymphocystis is a chronic disease of freshwater and marine fishes caused by infection with an iridovirus known as Lymphocystivirus or Lymphocystis disease virus (LCDV). Infection results in the development of pebble or wart-like nodules most commonly seen on the fins, skin, or gills, although other tissues may be affected. This 5-page fact sheet was written by Roy P. E. Yanong, and published by the UF Department of Fisheries and Aquatic Sciences, December 2010.
http://edis.ifas.ufl.edu/fa181