Dietary argan oil for juvenile rainbow trout: growth performance, fatty acid profile, and antioxidant defense

Abstract The sustainability of aquaculture is increasingly challenged by reliance on fish oil as the primary dietary lipid, raising concerns over cost, supply stability, and pressure on marine ecosystems. Plant-based oils offer promising alternatives, yet their effects on fish growth, lipid metabolism, and physiological health remain to be fully elucidated. Argan ( Argania spinosa L.) oil, rich in unsaturated fatty acids and bioactive antioxidant compounds, represents a novel feed ingredient whose potential in aquaculture nutrition has not yet been explored. This study assessed the replacement of dietary fish oil with argan oil at inclusion levels of 0 (control; AO0), 33 (AO33), 67 (AO67), and 100% (AO100) in juvenile rainbow trout ( Oncorhynchus mykiss ) over an 8-week feeding period. Growth performance, feed efficiency, and proximate composition were not significantly influenced by dietary treatments. On the other hand, increasing argan oil inclusion resulted in a gradual reduction of long-chain n-3 polyunsaturated fatty acids, particularly eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic (DHA, 22:6n-3) acids in fish. However, when fish oil was replaced with a relatively high level of argan oil as in fish fed the AO67 diet, these fatty acids were remained at reasonable levels (2.1 and 10.2%, respectively). Hepatic lipid peroxidation reduced with the increase in dietary argan oil level, reaching the lowest value (2.9 nM MDA/mg protein) in fish fed the AO100 diet. The overall results suggest that argan oil can totally replace fish oil in rainbow trout diet without compromising growth and feed utilization. It is noteworthy that the sustained growth and feed utilization at total replacement may be attributed to residual dietary n-3 LC-PUFAs provided by fishmeal and the relatively limited trial period. Therefore, to ensure sustainability over long-term feeding practices, partial replacement at 67% is suggested, as this level enables fish to maintain comparable n-3 LC-PUFAs retention, optimal growth and feed utilization, and enhanced oxidative defense.