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Abstract
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The effects of dietary n-3 highly unsaturated fatty acids [eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA)] with ?-tocopherol on growth, non-specific immune response and oxidative status were investigated in Caspian brown trout, Salmo trutta caspius, fry. Six experimental diets containing three different dietary levels of n-3 HUFAs (low: 1 0.5% of total fatty acids, DHA EPA, medium: 2 1%, DHA EPA, high: 4 2%, DHA EPA) with two different levels of ?-tocopherol (low: 300 and high: 1000 mg kg?1 diet) were prepared and named: LL, LH, ML, MH, HL and HH (HUFA/?-tocopherol) groups, respectively. Diets were fed to triplicate groups of 60 fry with an initial weight of 600 ± 25 mg for 10 weeks. Results showed that increase in dietary DHA and EPA up to high level improved fry growth in terms of the body weight and specific growth rate, particularly when dietary ?-tocopherol levels were high, suggesting a higher antioxidant protection value when these fatty acids are high. At all dietary n-3 HUFA levels, increase in ?-tocopherol from low to high level enhanced the alternative complement (ACH50) activity. Fry fed diets medium and high n-3 HUFA displaying significantly higher lysozyme activity (P < 0.05). Moreover, fish fed medium or high levels of n-3 HUFA had significantly lower prostaglandin E2 (PGE2) than those fed low n-3 HUFA (P < 0.05). Significant differences in antioxidant enzymes (catalase, glutathione peroxidase, glutathione S-transferase, glutathione reductase and superoxide dismutase) activity were also observed between groups, with higher activity in high levels of n-3 HUFA (P < 0.05). Results of this study suggest that the effect of dietary n-3 HUFA on examined non-specific immunity parameters are not uniform; however, these impacts are closely related to the ?-tocopherol supplement and their interaction. In conclusion, increased dietary levels of n-3 HUFA and ?-tocopherol would enhance growth performance and welfare of this species.
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