Transmission

The major routes of transmission appear to be via infected fish, contaminated water and feeding of trash fish. Although the disease causes mortality in fish as small as 10 g, fish are mostly susceptible above 100 g. The greatest losses occur in large fish close to market size. Outbreaks can occur all year round but are usually triggered by environmental stress to the fish, for example, due to overcrowding and changes in water quality. 

Most fish farmed in Asia are susceptible to this disease. A selection of these are listed below: