A DNA vaccine against infectious hematopoietic necrosis virus (IHNV) was the first DNA vaccine developed for use in salmonid fish. Protective immunogenicity was only observed with the glycoprotein (G) gene in rainbow trout Oncorhynchus mykiss using the DNA vaccine technology. A similar significant level of protection was also observed in Atlantic salmon Salmo salar vaccinated with a naked plasmid encoding the G protein and assessed for protection by immersion and cohabitation IHNV challenges. In both studies vaccinated fish seroconverted and this sera was shown to be protective after passive transfer and subsequent challenge with IHNV. Vaccine doses as low as 1-10 ng provided significant protection to rainbow trout fry (mean weight, 0.8-1.8g) and an optimal dose of 0.1 μg was selected. Rainbow trout immunized with this dose were shown to significantly protected against a broad range of viral strains from different geographic locations and host species. Although intramuscular injection is the principle mode of vaccination, gene gun immunization induced protective immunity in fry, while intraperitoneal injection provided partial protection. This vaccine was also shown to provide significant protection as soon as 4 days after intramuscular vaccination and provided a significant level of crossprotection against another fish rhabdovirus, viral hemorrhagic septicemia virus, for a transient period of time.