NMR metabolomics and lipid analyses in salmonid tissue
Abstract: Salmonids are fatty fish and contain high amounts of omega-3 polyunsaturated fatty acids, beneficial in human nutrition. However, the aquaculture industry has expanded greatly in recent decades, increasing demand for fishmeal (FM) and fish oil (FO) for fish feed, while the supply of fish raw materials has remained static or declined. This has created a need for alternative sustainable raw materials for fish feeds. This thesis examined the effect of replacing FM or FO with alternative plant (vegetable oils (VO), sesamin), microbial (zygomycete-, yeast fungi) and marine (krill, mussel) raw materials on growth performance, lipid content, fatty acid composition, lipid classes and fish metabolism in Atlantic salmon (Salmo salar) and Arctic charr (Salvelinus alpinus). There was a significant negative effect on growth performance when sesamin, zygomycete fungi and extracted yeast were included in fish diets. Replacement of FM or FO with alternative materials affected the lipid profile in fish tissues, e.g. compared with the control, docosahexaenoic acid (DHA) level was higher in fish fed krill meal and mussel meal and lower in fish fed VO, but unaffected in fish fed extracted and non-extracted yeast and sesamin. Zygomycete fungi meal inclusion decreased fish lipid content, thereby increasing DHA by 54% of total lipid content. Metabolomics analyses revealed an effect on several metabolites depending on the diet. Inclusion of sesamin increased the levels of some metabolites associated with energy metabolism, suggesting metabolic disturbance in the fish. Replacement of FM with non-extracted yeast affected liver metabolites, while extracted yeast mainly increased muscle metabolite levels. These increases suggested that the test ingredients produced a significant response in fish muscle metabolism. The altered metabolic fingerprint in fish fed krill and mussel meal diets compared with FM suggested differences in ingredient composition and physiological response to the diets. These results provide new information on the effects of non-traditional ingredients on fish metabolism, e.g. lipid-, single-carbon metabolism and tricarboxylic acid cycle. More studies are needed to identify the biochemical mechanisms involved and commercialise alternative fish feed materials.
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