Evaluation of Yersinia ruckeri vaccine performance in rainbow trout (Oncorhynchus mykiss)

Yersiniosis is one of the most important bacterial diseases that cause a lot of economic losses to cold-water fish farms in the country. Therefore, the use of effective vaccination is one of the best ways to control this disease. In this study, the vaccine efficacy of different methods of bathing in these fish has been evaluated. In this regard, 300 fish with an average weight of 3 ± 0.35 were divided into 12 tanks after adaptation. In this study, 6 experimental groups including a positive control group, negative control group, single dose vaccinated fish group, two-dose vaccinated fish group, hyperosmotic environment + single dose vaccinated fish group, and hyperosmotic environment + two-dose vaccinated fish group. Fish from different groups were exposed to 4.3 10 107 bacteria intraperitoneally after vaccination and the survival rates of the fish was evaluated.Based on the results, the white blood cells counts (WBC) in the vaccinated groups were significantly higher than the control group. Yersinia ruckeri antibody titers by microagglutination method were also measured significantly higher in the vaccinated groups compare to the control, in the othe hand, in the fish that received the vaccine twice, this titer was significantly higher than the other groups. According to the bacterial exposure results, 100% of the fish in the control group died during 5 days. In all vaccinated groups, the mortality rate was significantly lower than the control group, while the lowest mortality rate was recorded for fish in the hyperosmotic environment + twice vaccine. In this study, vaccination significantly reduced fish mortality after exposure to Yersinia rockeri bacterium, and based on this study, the use of hyperosmotic environments with vaccination is recommended to increase vaccine efficacy.