Efficacy and Antibody Titers Response of Rainbow Trout, Oncorhynchus mykiss Bivalent Vaccine Against; Streptococcus iniae and Yersinia rockeri

Streptococcosis and Yersiniosis are important diseases for the aquaculture industry for the rainbow trout (Oncorhynchus mykiss).  In this study, the specific immunological responses of rainbow trout to vaccination with the bivalent vaccine of Streptococcus/ Yersinios were investigated. Three hundred rainbow trout fingerlings (25±2g) were randomly divided into four equal groups in triplicates. Treatments contain Streptococcosis vaccine, Yersiniosis vaccine, bivalent vaccine, and control group.  Fish in vaccinated treatment intraperitoneally injected with 100 microliter vaccine on the first day. The control group was injected with sterile PBS, identical to the vaccinated group. Blood samples were collected from vaccinated and non-vaccinated groups at days 0, 30, and 60 of the study, and antibody titer was subsequently performed. Sixty days after initial immunization, all groups were challenged by a lethal dose of Streptococcus iniae and Yersinia rockeri, mortality rate was calculated and compared among the groups for 14 days. These results indicated high antibody levels in the vaccinated fish at day 30 and 60 post-immunization using both vaccines(p<0.05). However, this amount was fewer at day 60 than day 30. The percentage of trout cumulative mortality after the challenge with Streptococcus iniae and Yersinia rockeri showed a significant decrease in vaccinated groups compared to the control treatment. In general, it can be concluded that the administration of bivalent Streptococosis/Yersiniosis vaccine to the rainbow trout provided appropriate protection against disease and effectively induced the immune response against these two diseases, which is comparable to either of the vaccines separately.