Effect of Montanide™ IMS 1312 VG adjuvant on efficacy of Yersinia ruckeri vaccine in rainbow trout (Oncorhynchus mykiss)

The efficacy of immersion vaccination Yersinia ruckeri bacterin containing Montanide™ IMS 1312 VG was evaluated in 100-120 g rainbow trout against yersiniosis. Healthy fish were vaccinated by immersion vaccination with inactivated whole cells (1 × 108 cells/ml) of a virulent strain of Y. ruckeri biotype I with and without Montanide (1:1; Montanide/antigen) for 2 min at 12-14 °C. Control group was immersed in sterile PBS. Leukocyte counts, serum lysozyme assay, alternative hemolytic complement (ACH50) assay, antibody titration and relative percent survival (RPS) were measured on 2-10 weeks post-immunization. No significant difference was seen in leucocyte population of trout immunized either with Y. ruckeri antigen or Y. ruckeri antigen containing Montanide (P > 0.05), while leucocyte and heterophil populations in control group were significantly lower and higher, respectively, than both immunized groups (P < 0.05). In addition, there was no significant difference in lymphocyte population of trout immunized either with Y. ruckeri antigen or Y. ruckeri antigen containing Montanide (P > 0.05), while lymphocyte population in control group was significantly lower than both immunized groups (P < 0.05). Lysozyme activity in immunized fish with Y. ruckeri containing Montanide was higher than the immunized fish with Y. ruckeri antigen alone during 8 weeks post-immunization ((P < 0.05). Also, level of lysozyme in control fish was generally lower than both immunized groups (P < 0.05). The level of ACH50 between both immunized groups was insignificant (P > 0.05) but these were significantly higher than control group through the experiment (P < 0.05). The lowest anti-Y. ruckeri antibody titers in both immersion vaccination groups were significantly higher through 2-8 weeks post-vaccination compared to the control group (P < 0.05). In the group immersion vaccinated with Y. ruckeri bacterin plus Montanide the titers 2-8 weeks post-vaccination were significantly higher the titer in the immersion vaccinated with Y. ruckeri bacterin (P < 0.05). Fish vaccinated with antigen without Montanide resulted in RPS of 80-82% on 2-10 weeks post-vaccination, while those for antigen containing montanide gave RPSs of 93.8-100% 2-10 weeks post-immunization (P < 0.05).