Authors : M.E. Barnes, M.L. Brown, T.J. Bruce, R. Neiger and S. Sindelar
Abstract: This experiment evaluated the response of McConaughy strain rainbow trout Oncorhynchus mykiss fed isonitrogenous, isocaloric diets containing either 40% fish meal and no fermented soybean meal or 15% fish meal and 35% fermented meal, prior to and during a disease outbreak in a production hatchery. The trout were initially reared for 30 days in indoor circular tanks with negligible mortality. They were then moved to rectangular raceways and maintained on the same treatment diets. Mortality started 18 days later and continued for the next 7 weeks. Overall mortality was not significantly different between the groups fed either of the two diets and ranged from 2.16-8.11%. Although, visible and histopathological indications of Bacterial Coldwater Disease were observed, neither bacteriological culture nor molecular methods confirmed the presence of Flavobacterium psychrophilum. There were no significant differences in qualititative health assessments, viscerosomatic index or hepatosomatic index in fish fed either diet. Distal intestine inflammation was not observed in any of the fish and qualitative rankings of distal intestine morphology were not significantly different between the diets. Immunological sampling 25 days following the transfer to raceway cages indicated no significant differences in spleen somatic index, macrophage activity, respiratory burst or plasma lysozyme activity in fish fed either diet. These results indicate that feeding a diet with fermented soybean meal as the primary protein source will not lead to increased mortality during a disease event in rainbow trout, even if fish growth is negatively affected.
M.E. Barnes, M.L. Brown, T.J. Bruce, R. Neiger and S. Sindelar, 2015. Effects of a Fermented Soybean Meal Diet on Rainbow Trout Mortality and Immune Function During a Disease Outbreak. Journal of Aquaculture Feed Science and Nutrition, 7: 6-15.