The Influence of Substitution of Dietary Fish Oil with Different Vegetable Oils on Performance and Fatty Acid Composition of Brown Trout, Salmo trutta

Brown trout Salmo trutta (similar to 1 g) were fed four casein-gelatin based diets with different lipid resources for 6 weeks. The sources of dietary lipid were menhaden oil (MO diet), hazelnut oil (HO diet,), a blend of linseed oil and soybean oil (1:1) (LO+SO diet), and soybean lecithin (IF diet). Feeding trial was conducted in a recirculating water system at 13 +/- 0.2 degrees C. Fish fed LO+SO diet demonstrated the highest growth performance while those fed HO diet had the lowest growth rate (P<0.05). The fatty acid profiles of fish reflected the fatty acid composition of the diets. High level of docosahexaenoic acid (22:6n-3, DHA) in whole body lipids of fish fed LO+SO diet corresponded with the high level of linolenic acid (18:3n-3, LNA) in the lipids of this diet. Fish fed LE diet which was rich in linoleic acid (18:2n-6, LA) had the highest level of arachidonic acid (20:4n-6, ARA) in their body. The results suggest that the efficiency of elongation and desaturation of C18 fatty acids depends on the dietary lipid source and brown trout has capacity to transform LA and LNA to ARA and DHA, respectively. Growth depletion in fish fed HO diet might be caused by essential fatty acid deficiency.