Influence of oxidized lipids and hazelnut oil supplementation on growth, fatty acid composition and antioxidant defense system in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) with approximately 1 g initial weight were fed diet with different levels of fresh fish oil, oxidized fish oil and fresh hazelnut oil in a semi-recirculating water system equipped with biological filtration for 9 weeks. The feeding trial was carried out in triplicates and the temperature was 131°C during the experiment. At the end of the study, growth performance was significantly affected by the experimental diets (P <0.05). Fish fed diets with fresh fish oil grew significantly better than those fed diet with oxidized fish oil (P <0.05). Hazelnut oil supplemantation up to 60% of dietary lipids had possitive effect on growth performance while the fish fed diet with 100% hazelnut oil had the lowest growth. The fatty acid profile whole body fish was significantly influenced by the experimental diets. Polyunsaturated fatty acids showed significant decrease with both dietary hazelnut oil supplemantation and the use of dietary oxidized fish oil (P <0.05). The amount of total glutathione and superoxide dismutase enzyme activity in the liver fed experimental diets were significantly affected neither by the use of dietary oxidized fish oil or by the addition of dietary hazelnut oil. On the other hand, dietary hazelnut oil supplemantation caused a significant increase in hepatic vitamin E content whereas the level of lipid peroxidation (malondialdehyde) decreased significantly at the same circumtance (P <0.05). Our result suggest that substitution of fish oil up to 60% had positive effect on growth in rainbow trout. Moreover, we can conclude that hazelnut oil supplemantation can protect the fish against the problems caused by dietary oxidized fish oil.