Metabolomics as a tool to evaluate salmonid response to alternative feed ingredients

Aquaculture has largely expanded in the last decades to satisfy the growing market demands for fish products. Fishmeal and fish oil, which are traditionally used in salmonid feeds, are becoming unsustainable. Development of aquafeeds based on alternative ingredients are needed to overcome the ecological challenges. Importantly, when using the new diets, fish growth performance, fish health and food quality need to be considered. In the thesis, different substitutes of fishmeal and fish oil were evaluated by using NMR and MS-based metabolomics. The Baltic Sea is one of the most threatened water bodies and has environmental problems, such as contamination and eutrophication. The use of Baltic Sea-sourced nutrients after certain treatments in fish feeds would recycle the less valuable nutrients for human back into the food chain, and may promote an environmental-friendly aquaculture system. In the thesis, we found that use of detoxified fishmeal and fish oil reduced adverse effects on fish health related to energy metabolism and hepatotoxicity, compared with the untreated diets. Moreover, the decontaminated fish materials containing high content of n-3 fatty acids were found to be valuable sources of fish feeds. Additionally, a new Baltic blend diet composed of Baltic Sea-sourced decontaminated fishmeal, blue mussel and baker’s yeast was fed to Arctic char (Salvelinus alpinus) for 10 months. Based on the metabolomics results, the dietary content of betaine, trimethylamine-N-oxide and aromatic amino acids needs to be modified, in order to achieve a better growth performance. The hepatic metabolic heterogeneity of salmonids was also observed in the thesis. Furthermore, the sphingolipids in salmonids skin were characterized for the first time. We found that reduction in dietary levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) changed the fatty acid composition in glycerol-phospholipids subclasses and sphingolipid composition in skin of Atlantic salmon (Salmo salar). These changes potentially disturb the barrier function of fish skin. These findings provide new information on application of metabolomics in development of alternative aquafeeds