A dose-response study with omega-3 rich canola oil as a novel source of docosahexaenoic acid (DHA) in feed for Atlantic salmon (Salmo salar) in seawater; effects on performance, tissue fatty acid composition, and fillet quality

Long-chain omega-3 rich oils from crops genetically modified with algal genes are a promising new source of the omega-3 fatty acid DHA (docosahexaenoic acid; 22:6n-3) in Atlantic salmon diets. In this study, the fish oil and fish meal content were held constant across diets, and conventional canola oil was replaced with DHA canola (DHA-CA) oil in a step-wise manner at 0%, 25%, 50%, and 100% replacement, respectively. Growth of salmon, reared in seawater, from approximately 465 g to 1.5 kg was equal across all dietary treatments. Survival was > 98% in all cases, with no difference between the dietary groups. Digestibility of lipids was high, approximately 93% in all dietary groups. Fatty acid retention in whole body was also high, with greater retention of alpha-linolenic acid (ALA, 18:3n-3) and eicosapentaenoic acid (EPA; 20:5n-3) in groups containing higher proportions of DHA-CA oil. Fillet, liver, and intestinal fatty acid compositions were influenced by the different fatty acid contents of the diets, with progressively higher inclusion of ALA, EPA, and DHA and a higher n-3:n-6 ratio in fish fed the 25%, 50%, and 100% DHA-CA diets. Increased dietary inclusion levels of DHA reduced the conversion to 1-C-14 labelled ALA to 1-C-14 EPA in liver cells, but some conversion of ALA to 1-C-14 EPA was maintained even at high dietary DHA levels. There was also a significant increase in anti-inflammatory pro-resolving lipid mediators, resolvins, with increased dietary DHA-CA. The visual colour impression of both muscle and skin was improved at higher DHA-CA inclusion levels in diets. Overall, our findings demonstrates that DHA-CA oil is an effective ingredient in Atlantic salmon diets in seawater, and that fatty acids (FA) from this oil are incorporated into the fish tissues in a manner equivalent to FA from conventional sources, with positive effects on fillet quality.