In order to study the immunogenic and protective effects of DNA vaccine,plasmid DNA encoding flagellin flaC gene(designated as pcDNA-flaC)was used as a DNA vaccine to immunize red snapper(Lutjanus sanguineus).The distribution,expression and immunoprotection of the DNA vaccine were analyzed in tissues of the red snapper by PCR,RT-PCR and challenge test.PCR results indicated that pcDNA-flaC was distributed in liver,spleen,kidney,gill and injection site muscle at 7-28 days after vaccination.RT-PCR results indicated that the flaC gene was expressed in all above tissues of vaccinated fish at 7-28 days after vaccination.These results demonstrated that the DNA vaccine was distributed and flaC gene was expressed in various tissues of vaccinated fish.Red snapper immunized with DNA vaccine showed higher serum antibody levels at 7-28 days after vaccination,compared to fish vaccinated with the control eukaryotic expression vector pcDNA3.1 and PBS.In addition,fish immunized with DNA vaccine developed a protective response to live V.alginolyticus challenge 28 days post-inoculation,as demonstrated by increased survival of vaccinated fish over the control fish.This study indicates that pcDNA-flaC is an effective vaccine candidate against V.alginolyticus infection.