Effect of three administration routes of streptococosis/lactococosis Bacterin on specific immunity and expression of IgM and IL-6 genes in rainbow trout

In this study the effect of streptococosis/lactococosis bacterin administrated via oral, bath and intraperitoneal routes on the expression of two immune related genes (IgM and IL-6) was investigated. 600 fish (14±2.1g) were randomly divided into 4 groups in triplicates. Group 1 was vaccinated via oral route using 108CFU bacterial cell (Streptococcus iniae and Lactococcus garvieae) in each gram of food. Group 2 was injected with 0.1mL of 109CFU/mL bacterin. Group 3 was vaccinated via immersion route for 2 minutes in 109CFU/mL. Group 4 was none immunized group without vaccination. Fish were reared for two months in a similar situation. At days of 0, 20, 40 and 60, antibody titer against both bacteria was performed by ELISA method and expression of IL-6 and IgM genes were evaluated through qRT-PCR method. Then fishes were exposed to S. iniae and L. garvieae separately at the end of the experiment and the rate of mortality was compared among the groups. The result showed that the rate of mortality in exposed fish to S. iniae in injection, oral, immersion and unvaccinated routs were 20±10,  56.3±10, 50±5.67 and 90±3.67 whereas in exposed fish to L. garvieae were 26.67±5.77, 57.7±10, 43.33±5.67 and 90± 4.63 respectively. The antibody titer in the vaccine injection group was increased compared to control (P<0.05). Expression of IL-6 and IgM in vaccinated groups was significantly increased compared to the control group (P<0.05) with the highest rate in the injection group. It can be concluded that although injection route causes the best protection, antibody titer and expression of immune genes, oral and immersion routes could also induce relative protection and immunogenicity in rainbow trout and each route possesses some priority over other routes then further research on efficacy improvement of each route can be recommended.