Lymphocystis is a viral disease which affects the fishes in the aquarium. The herpes virus causes this disease. You need not worry about this viral disease as it is not a deadly disease. It is very rare to get this infection on the fishes in the aquarium. Only if this virus is introduced in the aquarium it will be affect the fish. Otherwise the chances of infection due to Lymphocystis are very rare. This virus is introduced mostly by adding new fish to the aquarium that is already affected by the virus. So if you quarantine any new fish for a few weeks before adding them to the aquarium, the chances of introduction of Lymphocystis is meager. Apart from adding fishes, it is also better not to add water from other aquariums to the one that you have. The water that you add might be infected with this virus. Gold fish and Koi are those that are affected mostly by this viral disease.
Some might be feeding the fish with live foods. Live foods are one of the other carriers of Lymphocystis. Hence it is better to avoid giving live foods that you get from other places. If you cultivate the live food at home then you can very well give those live foods to the fishes. Do not get live foods from other places as it might contain Lymphocystis. Home cultivated live foods reduced the risks involved in acquiring Lymphocystis and other diseases.
The fish that is infected with Lymphocystis will get small swellings in white color in the body and the fins. This is one of the symptoms of Lymphocystis. The tumor caused by Lymphocystis could look like a cauliflower in some cases and in other cases it can grow to the size of an egg too. During the initial stages of this infection when the tumor is small you would not find any difference in the color of the skin. As the tumor grows, you can see it in the red or purple color distinct from the skin color. Most of the fishes recover by themselves from this disease. The immunity present in the fish will cure itself. This is one of the reasons not to fear about Lymphocystis. If you find any fish that is affected by Lymphocystis then it is better to move them to a separate tank leaving them to recover by themselves. Although it is not a fatal disease it is sure that the health of the fish is affected. This might pave the way for other deadly diseases to be acquired by the fish. Hence monitoring of the fish affected by Lymphocystis is essential. There are medications sold in the market for this condition but is those medications are of no use. It is better to leave it alone so that they recover by themselves.