| Summary: | Flavobacterium psychrophilum is the etiological agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS). Current prevention strategies are limited and disease treatment primarily relies on antibiotics. As concerns about antibiotic use increase so too does the search for alternative treatment and prevention methods. In this study, testes meal from pink salmon, Oncorhynchus gorbuscha, testes collected from Alaskan seafood processing byproducts was supplemented in diets to determine effects on growth and immune function of rainbow trout, Oncorhynchus mykiss. Three diets were formulated for this study: a diet containing 5% testes meal, a diet containing a �-glucan immunostimulant (Macrogard) and a control diet. Each diet was fed to triplicate groups of juvenile rainbow trout for 12 weeks, at which time they were challenged with F. psychrophilum. No significant differences in growth were observed. Intermittent increases in phagocytic activity were observed in fish fed the testes meal. At 12 weeks; however, the phagocytic activity was significantly lower in fish fed the testes meal and Macrogard diets. Fish fed the testes meal and Macrogard diets also had significantly lower (P < 0.05) antibody titers at 8 weeks post challenge. These findings suggest suppression of the innate immune response following long term application impaired the adaptive immune response. To further investigate potential feed additive benefits, this study also examined the long term use of the probiotics Enterobacter sp.strains C6-6 and C6-8 in combination with an attenuated F. psychrophilum vaccine. In the first challenge, rainbow trout fry were fed a diet top-coated with C6-6, C6-8 or a combination of the two from first feeding and challenged at 54 days post hatch with a virulent strain of F. psychrophilum. Following challenge there were no significant differences in the cumulative percent morality (CPM) between any of the treatments, suggesting long term feeding of these probiotic strains may have limited ...
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