Interferons ( IFN s) have been reported in vertebrates from fish to mammals. To date, two types of IFN s, i.e. type I and type II IFN s have been reported in a range of fish species in aquaculture. In fish, type I IFN s are clarified into group I and group II , with two cysteines and four cysteines, and further into subgroups a, d, e, h, and b, c, f, respectively. Group I IFN s appear to exist in all fish species, whereas grou...