Recently, it was reported that a single vaccination (intramuscular injection) with NNV VLPs produced in Escherichia coli (1.5 mg/g) was enough to provoke a high titer of neutralizing antibody (Liuet al., 2006). In the present study, fish receiving one
(relatively low) dose of 0.6 mg/g of RGNNV VLPs produced high titers of neutralizing antibody (Table 1 and Fig. 2B) and all the fish survived challenge with 109 TCID50 of NNV (Fig. 3).