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The effect of oxidized dietary lipid and vitamin E on growth and immunocompetence of coho salmon (Oncorhynchus kisutch) Forster, Ian


Highly unsaturated marine lipids are common ingredients in salmon diets, and they are prone to oxidative change. The present study was undertaken to examine the growth and health of coho salmon (Oncorhynchus kisutch) fed diets containing herring oil autoxidized to different degrees. The efficacy of dietary vitamin E in ameliorating any adverse effect on performance was investigated. Herring oil was oxidized to one of two levels (relative to a control) by aeration and mild heating (40 °C). Peroxide values and iodine numbers were recorded to monitor the extent of autoxidation. Depletion of dietary linolenic acid series fatty acids (n3FA), and the labile vitamins A, C, and E, provided further evidence of the progress of lipid oxidation. The mean initial body weight was 5.1 g/fish, and growth (weight and length) was measured at 3 or 6 week intervals for 28 weeks. Experimental diets contained 16.8% lipid, primarily as herring oil. One diet was made with corn oil replacing herring oil, and another contained a combination of low and highly oxidized oil. Vitamin E (as dl-ɑ-tocopheryl acetate) was added at either 30 IU/kg dry diet or 1000 IU/kg dry diet. At 23 weeks, 1/3 of the fish were vaccinated against vibriosis. At 28 weeks the fish were twice challenged with live Vibrio sp. Immunocompetence was estimated by mortality and by plasma agglutination. The inclusion of autoxidized herring oil reduced the nutritive value of the diets. The poorer growth and feed efficiency of fish fed diets containing oxidized oils appears to have resulted from a combination of appetite suppression and nutrient deficiency. The relative importance of these factors in influencing growth and feed efficiency depended upon the extent of the oxidation, with appetite suppression being most apparent in fish fed diets containing moderately oxidized oil. Dietary supplementation with a high level of vitamin E had no ameliorating effect on growth or feed efficiency. Health and immunocompetence were not impaired by the presence of oxidized dietary lipid, or improved by the addition of vitamin E.

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