Effects of two-strain streptococcosis vaccine “Streptococcus iniae / Lactococcus garvieae” on some serum immune parameters in rainbow trout “Oncorhynchus mykiss”

Streptococciosis is one of the most common bacterial diseases in cold water fish farms in Iran that causes a lot of losses to these farms every year and vaccination can be very effective in controlling this disease. In this study, the effectiveness of streptococcus/lactococcus vaccine was evaluated in both injection and bath methods in rainbow trout (Oncorhynchus mykiss) fingerling. For this purpose, four treatment groups include one-step vaccinated using the bath method group, two-step vaccinated using the bath method group, hyperosmotic fish group+two-step vaccine using the bath method, the group of fish vaccinated with the injection method, and a control group considered. In this regard, 350 fish with a weight of 4.2±0.36 were divided into 10 tanks (two replicates for each group). The fish were reared and tested for two months. In this study, 5 experimental groups including the control group, the group of one-stage bath vaccination fish, the two-step bath vaccination group, the group of fishes vaccinated with hyperosmotic environment+two-step bath vaccination, and the group of vaccination via injection method. Based on the results, total serum protein levels in all vaccinated fish were higher than those in the control group, and based on statistical analysis, the highest level was recorded in the fish vaccinated by injection and the two-stage hyperosmotic+vaccine bath method. Glucose values were also measured in both groups of two-step vaccinated fish and the injection method was higher than in other fish. The ALP, ALT, and AST levels in the injected fish group were higher than those of the other groups. Finally, the serum antibody levels for both Streptococcus iniae and Lactococcus garvieae bacteria was higher for the fish in the injection group and the two two-stage bath groups than the one-stage vaccinated fish. At the same time, no antibody was observed in the control group. Based on the results, the two bath steps vaccination more and less produces the same levels of serum antibody titer as the injection method in fish, at the same time, the bath method caused less injuries compared to the injection method in fish. So in situations where fish are under stress, bath vaccination with reminder doses can be critical and more effective.