From The Aquarium Wiki
Lymphocystis is a common iridovirus disease of freshwater and saltwater fish. Virtually all shop bought fish may already have this.
Aquarists often come across this virus when their fish are stressed such as when put into a new environment and the virus is able to grow due to a impaired immune system.
The fish starts growing small white pin-prick like growths on their fins or skin and this is often mistaken for Ich (Ichthyophthirius multifiliis) in the early stages. It soon clumps together to form a cauliflower-like growth on the skin, fins, and occasional gills.
There is no known cure for this virus, though some aquarists recommend surgery to remove the affected area if it becomes very serious.
- (Acriflavine is said by some to cure this virus. But there is no solid evidence that it does little more than help heal the skin and fins. It can't remove the virus.
- Applying Ich treatments will not work!
- Lymphocystis is transmitted by direct contact with infected individuals.
If the virus continues to spread then the growths can inhibit the fish's ability to swim, breathe or eat, and secondary bacterial infections can kill the fish.
It can happen that the virus will not spread and will remain ever present and the fish can live a normal life as long as its swimming, breathing or eating is not affected.
Usually the best cure is to simply give the fish a stress free life, good diet and water quality and perhaps a weekly bacteria treatment and the virus will hopefully slowly subside and the fins will repair themselves. This can take many months however.