Performance, skin and gut health, and fillet quality in Arctic-farmed Atlantic salmon – Effects of increased EPA + DHA and organic zinc source in feed

Summary

Atlantic salmon farming in Arctic regions faces challenges due to extreme environmental conditions. Ulcerative diseases and infections are common health issues, often linked to low seawater temperatures and limited knowledge on nutritional requirements. Long-chain omega-3 fatty acids, EPA and DHA, are essential for immunity, robustness and good fillet quality, and may also affect zinc (Zn) bioavailability important for wound healing and well-functioning mucosal barriers. Hence, this study aimed to assess the potential beneficial effects of increasing dietary EPA + DHA from standard 7.5 % to 10 % of total fatty acids, combined with two organic Zn sources, standard (sZn), and Zn with increased bioavailability (AvZn), in diets for Atlantic salmon reared in the Arctic region. A full-scale seawater feeding trial was conducted at a commercial site in Finnmark, Norway, from September 2020 to harvest in November 2021. Growth, performance, skin and intestinal health, fillet composition and quality, and welfare were evaluated at four timepoints. Increasing dietary EPA + DHA from 7.5 % to 10 % resulted modest overall benefits. Both groups showed similar growth and performance. Higher EPA + DHA levels improved fillet nutritional value and quality with greater EPA + DHA deposition, higher firmness and lower black spot prevalence, and reduced fin damage. Differences between the two Zn sources in 10 % EPA + DHA diets were minimal. AvZn increased fillet firmness while sZn improved welfare indicators by rescuing scale loss, skin lesions/wounds and snout damage. This study suggests that 7.5 % dietary EPA + DHA is sufficient for optimal growth and performance yet increasing it to 10 % can improve fillet quality and nutritional value. The two Zn sources had distinct benefits.