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Affected fish

Most freshwater fish except members of the cyprinid family. Fish that have been artificially coloured through the cruel process of injection dyeing are particularly prone.


Viruses belonging to the iridovirus group. The virus is released from infected fish and can survive for many days in the water, during which time it can infect other fish. Fish with open wounds or damaged areas of the body are liable to become affected if the virus is present in the water or in other fish. Some strains are more likely to affect fishes of a similar type.


The virus causes a massive enlargement of infected cells, creating a visible lump, nodule or growth usually a few millimetres in diameter. The enlarged areas are usually white, grey, or pinkish and may also appear internally, where they are not visible.


With the exceptions of quarantining new fish and using ultraviolet sterilisation to prevent transmission, there is no easy way to prevent infections.


There is no chemical treatment available, however, if affected fish are kept in a healthy and suitable environment, they will usually eventually fend of any infection although this may take several weeks or months.

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