Dietary substitution of fish oil with plant oils in juvenile black sea trout Salmo labrax (Actinopterygii, Salmoniformes, Salmonidae): Implications for growth, lipid metabolism, and tissue fatty acid quality
Abstract
Global fish oil production has plateaued while salmonid aquaculture expands, creating urgent demand for sustainable alternative lipid sources. This study evaluated the effects of replacing dietary fish oil with canola oil, safflower oil, and their blends on growth performance, feed utilization, condition indices, and muscle fatty acid composition in juvenile Black Sea trout, Salmo labrax Pallas, 1814. Seven isonitrogenous and isolipidic diets (45% crude protein, 18% crude lipid) differing only in lipid source—fish oil (FO), safflower oil (SO), canola oil (CO), and their 50:50 binary and equal ternary blends—were fed to triplicate groups of juvenile Black Sea trout (initial weight 30.22 ± 0.19 g) for 90 days. Growth performance, feed utilization, condition indices, and fatty acid compositions of diets and white dorsal muscle were determined. Growth performance and feed utilization did not differ significantly among treatments ( P > 0.05), confirming that complete fish oil replacement did not compromise growth performance. However, significant differences were observed in fat deposition rate, viscerosomatic index, and hepatosomatic index ( P < 0.05). Muscle fatty acid profiles closely mirrored dietary composition: saturated and n-3 long-chain polyunsaturated fatty acids (EPA, DHA) declined while monounsaturated and n-6 fatty acids increased with increasing plant oil inclusion. The muscle n-3/n-6 ratio fell most sharply in the safflower oil group. Economic analysis revealed that complete plant oil substitution reduced feed costs by 12%–13% compared to the fish oil control. Both canola and safflower oils can effectively replace fish oil in Black Sea trout diets without compromising growth. Canola oil emerges as the more broadly balanced substitute, while safflower oil’s strong n-6 enrichment restricts its suitability to blended or finishing strategies.