LAUSR

Abstract The use of microbial oil, high in docosahexaenoic acid (DHA), was investigated as a lipid source in diets for farmed Atlantic salmon. Schizochytrium sp. oil is produced from heterotrophic fermentation and it can be a renewable source of long-chain n-3 fatty acids due to its high DHA content. A 16-week feeding trial was conducted on Atlantic salmon (24 g initial weight) in freshwater to test the effects of microbial oil (MO) from Schizochytrium sp. (T18), on fish growth performance and tissue lipid and fatty acid composition. Four experimental diets were tested: a reference diet (20% FO) and a commercial-type control diet (10% FO + 10% vegetable oil), a low MO diet (5% MO) and a high MO diet (10% MO). There were no differences in weight gain (81–98 g), condition factor (1.08), specific growth rate (1.30–1.53%/day), nor feed conversion ratio (0.84–0.90) among all treatments (p > 0.05). Fatty acids in total lipid in the muscle reflected the fatty acid profile in the diet, particularly in salmon fed low and high MO diets, with high muscle storage of DHA and low EPA compared to salmon fed the FO and FO/VO control diets. Overall, Schizochytrium sp. (T18) is a candidate for use in dietary oil blends for juvenile salmon.