| Summary: | Docosahexaenoic acid (DHA) is essential for the normal growth of Atlantic salmon, with fish oil (FO) being the primary source. The expanding aquaculture industry increases pressure on wild fish stocks, necessitating novel and sustainable DHA sources. Aurantiochytrium limacinum, a microbial organism, holds potential as an alternative DHA source for aquaculture. This study aims to assess A. limacinum potential as a novel DHA source for Atlantic salmon, considering factors such as fish performance, nutrient digestibility, nutrient retention, and utilization. Pre-smolt Atlantic salmon were fed one of four experimental diets for nine weeks. Diet 1(control) was a commercial-like diet based on fish meal and soy protein concentrate as main protein source, and FO and rapeseed oil as fat sources. Diets 2-4 included A. limacinum at 5%, 10%, and 15%, respectively, with equal FO to meet DHA requirements. No differences in feed intake were observed across dietary groups. However, fish fed the highest inclusion level of A. limacinum (15%) showed reduced growth performance. Apparent digestibility of total fat and DHA also decreased in fish fed higher levels of A. limacinum. Despite these results, the study using cold-pelleted diets provides a foundation for future research on novel DHA sources. The findings suggest that moderate inclusion levels of A. limacinum can support sustainability in aquaculture. Further optimization of its production and processing could enable higher FO replacement levels as a DHA source for Atlantic salmon.
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