Effect of dietary conjugated linoleic acid levels on growth performance, muscle fatty acid profile, hepatic intermediary metabolism and antioxidant responses in genetically improved farmed Tilapia strain of Nile tilapia Oreochromis niloticus

Abstract

An 8-week feeding trial was conducted to determine the effect of dietary conjugated linoleic acid (CLA) on growth performance, muscle fatty acid profile, hepatic intermediary metabolism and antioxidant responses in genetically improved farmed Tilapia (GIFT) strain of Oreochromis niloticus (initial body weight: 42.6 ± 0.4 g, mean ± standard deviation). Three replicated groups of GIFT strain of Nile tilapia were hand-fed to satiation, twice a day, with the diets in which CLA oil, containing mainly the bioactive cis-9, trans-11 and trans-10, cis-12 isomers, was included at 0 (control), 0.5%, 1%, 1.5%, 2% and 2.5%, respectively, at the expense of fish oil to maintain the constant lipid and energy levels. Growth performance and feed utilization showed no significant differences among the treatments (P > 0.05). The dietary inclusion of CLA modified total percentages of the main groups of fatty acids. Increasing saturated fatty acid content and reduced mono-unsaturated fatty acid contents in muscle were observed with increasing dietary CLA inclusion (P < 0.05). Total n-3 fatty acids and total polyunsaturated fatty acids tended to decline with increasing dietary CLA levels (P < 0.05), but n-6 fatty acids showed no significant differences among the treatments (P > 0.05). Dietary CLA supplementation resulted in the significant increase in the trans-10, cis-12 and cis-9, trans-11 CLA isomers in muscle (P < 0.05) and also significantly influenced several hepatic enzymatic activities, such as succinate dehydrogenase, lactate dehydrogenase, malic dehydrogenase, lipoprotein lipase and hepatic lipase activities (P < 0.05). Reduced superoxide dismutase and glutathione peroxidase activities, and the decline in malondialdehyde levels were observed in fish fed the CLA-supplemented diets (P < 0.05), indicating that dietary CLA supplementation showed a powerful antioxidant effect for this fish species. Our study was the first report involved in the effect of dietary CLA inclusion on hepatic intermediary metabolism and antioxidant responses in fish, which could be used as indicators of nutritional and physiological status of the fish species.