Mortality rate and immune responses of rainbow trout (Oncorhynchus mykiss) infected with Yersinia ruckeri subsequent to feeding on diet supplemented with Ducrosia anethifolia essential oil

Application of the immunostimulant is the most promising method for controlling diseases in aquaculture. In this study, the mortality rate and immune responses of rainbow trout (Oncorhynchus mykiss) fed on diet supplemented with Ducrosia anethifolia essential oil was investigated after challenging with Yersinia ruckeri. The essential oil mixed with sunflower oil at different concentrations (0.001, 0.01 and 0.1%) and the commercial food was coated with this oil. Fish were fed with diets for 8 weeks and infected with Y. ruckeri at the ending of feeding trial. Serum protein, albumin, globulin and lysozyme and bactericidal activity of challenged fish were evaluated one week after injection and mortality were counted till day 10. The results showed that albumin had not differed among treatments. The highest level of the protein and globulin were found in control group. Serum lysozyme activity showed no difference between groups. The highest and lowest serum bactericidal activity was observed in 0.001% and control group, respectively. The mortality rates in infected fish were as 55% in control group, 40% in 0.001%, 70% in 0.01% and 70% in 0.1% treatment. Lowest rate of mortality was observed in group 0.001%, while began two days earlier than other groups.