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Effects of Vitamin Nutrition on the Immune Response of Hatchery-Reared Salmonids

Final Report 1989

Document format: pdf

Publisher: U.S. Department of Energy

Creation date: 1989

The objectives of this study were to define the dietary concentrations of folic acid, pyridoxine, riboflavin, pantothenic acid, ascorbic acid, and alpha-tocopherol required to assure maximum immune responses and resistance to Aeromonas salmonicida and Renibacterium salmoninarum in juvenile spring chinook salmon (Oncorhynchus tshawytscha). In the first year of the study a number of in vitro assays were evaluated - - as tools for measuring the immunological status of juvenile chinook salmon. Those assays included: response of lymphocytes to mitogens, mixed lymphocyte reactions, migration inhibition factor, measures of phagocytosis, plaqueforming cell counts, and polyclonal activation. The plaque-forming cell and mitogenic stimulation assays were selected as the most appropriate tests to use in our scheduled studies to evaluate the effects of vitamin nutrition. The plaque-forming cell assay measures the capacity of lymphocytes to produce a specific immune response to an antigen, while the mitogen assay measures the general immunocompetency of an entire population of lymphocytes. Also, the technical requirements for both of these measurements made it practical to perform the tests on the large number of fish involved. During the final three years of the project, graded levels of the test vitamins were incorporated in both the Oregon Test Diet and the Abernathy Diet and fed to small groups of spring chinook salmon juveniles. The fish were held in constant 12' well water under laboratory conditions for up to six months. During that period, the fish's immunocompetency was measured using plaque-forming cell and mitogenic assays. In addition, their resistance to laboratory challenges with Aeromonas salmonicida and Renibacterium salmoninarum was determined. Results indicated that the dietary levels of the test vitamins recommended for maximum growth by the National Research Council (NRC) were ample for growth and immunological function under our laboratory conditions. In fact, evidence indicated that, in some cases, concentrations of individual vitamins as low as one third of the NRC recommendation were adequate. The findings suggest that the NRC recommendations should be re-examined and refined. In the majority of cases, the values of the immunological parameters significantly increased with fish age or size. Further experiments will be required to determine the degree to which each factor is important. The results also suggest that attempts to immunize fish may be most successful if they are performed when the fish are older than six months. It should be noted that there was considerable variation in immunological measurements among fish within replicate lots fed individual diets. This has important implications for the immunological competency of significant segments of fish populations in hatcheries.

Key Words: DOE • Finfish Disease • Vitamin Treatments • Salmon