Viral I know of no effective treatment except to remove nodular growths by scraping. Fungal A secondary infection at the site of some other fish injury. Also affects damaged or disturbed fish eggs. Monogenetic Flukes Ich Trichophyra Internal parasites Most fish carry some parasites, but develop a degree of resistance that prevents problems. On the other hand, parasites such as anchor worms and fish lice usually are a problem whenever present.
Young fish are more susceptible to illness caused by parasites.
Some parasitic infections can be mistaken for bacterial diseases or viral infections and some may cause tumors. Treating fish diseases is sometimes a haphazard affair because we do not always exactly know what the fish is suffering from. Treatments for Koi diseases are still relatively unsophisticated. There are no funds available in the U.S. for the development of ornamental fish medicine. Dead fish decompose very rapidly and generally are of little diagnostic use even if they have been frozen.