Maternal Immunity Transfer of Zebrafish (Danio rerio) following Vaccination with a Live-Attenuated Vibrio harveyi Vaccine

Vibriosis causes a major setback in the marine aquaculture industry. In controlling vibriosis, vaccination of the broodstock could help in transferring the initial immunity to the fry and perhaps giving immunity to them during the culture period. This study determines the efficacy of three live-attenuated Vibrio harveyi vaccine (LAVh) derivatives on zebrafish broodstock in providing immunological protection to their offspring against pathogenic Vibrio spp. Zebrafish were vaccinated intraperitoneally with full effective dose (ED80) and monitored for 14 weeks. On week 6, the specimens were intraperitoneally (i.p.) challenged with pathogenic 10(7) CFU/ml of Vibrio spp., and subsequently another batch was left to spawn. Thereafter, the antibody level of larvae was monitored for 4 weeks post-hatching. Groups of juvenile zebrafish were given booster vaccination via immersion (1 x 10(7) CFU/mL) with vaccines similar to their predecessor. The fish were sampled weekly for four weeks to determine their antibody profile and pro-inflammatory gene expression. Finally, at week 3, the juvenile fish were challenged with pathogenic strains of Vibrio spp. Results of antibody profiling in the adult zebrafish model indicated that freeze-dried and stale LAVh delivers a longer immunological protective duration, while the FKVh vaccination group failed to provide immunological protection against V. alginolyticus. However, the gene expression of pro-inflammatory interleukin 1 beta (IL-1 beta) in the FKVh vaccinated group was elevated longer than that in the freeze-dried LAVh vaccinated group. Nevertheless, the relative percent survival (RPS) of both vaccination groups against pathogenic Vibrio spp. displayed 100% immunity. Overall, the freeze-dried LAVh vaccine was found to confer maternal immune protection for its offspring, provide a long duration of immunological protection and cross-protection coverage against pathogenic Vibrio spp., and have a longer shelf life. It is proposed to be commercially available for farmers to protect against Vibrio spp. infection.