Can Dietary Hazelnut Oil Inclusion Alleviate the Negative Effects of Oxidized Fish Oil in Rainbow Trout (Oncorhynchus mykiss) Juveniles?

Rainbow trout juveniles were fed different levels of fresh fish oil, oxidized fish oil and fresh hazelnut oil for 9 weeks. Growth performance and feed efficiency was significantly influenced by oxidized fish oil (P<0.05), but not by hazelnut oil supplementation and their interaction. Fish fed diets containing fresh fish oil had better growth and feed efficiency than those fed diets containing oxidized fish oil. Digestibility decreased with the increase in both dietary oxidized fish oil and hazelnut oil. Fatty acid profile in whole body lipids was significantly influenced by the experimental diets (P<0.05). Polyunsaturated fatty acids (PUFA) showed significant decrease with both dietary hazelnut oil inclusion and dietary oxidized fish oil. Dietary hazelnut oil resulted in a significant increase in hepatic vitamin E and a significant decrease in lipid peroxidation level (P<0.05). Our overall results suggested that dietary oxidized lipids caused growth depletion, lowered nutrient digestibility, lipid peroxidation, and decreased eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) levels in rainbow trout. However, dietary hazelnut oil inclusion alleviated the negative effects of oxidized oil, sparing n-3 long-chain PUFAs such as EPA and DHA, and increasing hepatic α-tocopherol level which lowered lipid peroxidation despite no significant impact on growth.