Effect of conjugated linoleic acid on dietary lipids utilization, liver morphology and selected immune parameters in sea bass juveniles (Dicentrarchus labrax)

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Increased energy content in fish feeds has led to an enhanced fat deposition, particularly in European sea bass, concerning fish farmers. Inclusion of conjugated linoleic acid (CLA) could reduce fat deposition as in other vertebrates. To determine if dietary CLA affects fat deposition, lipid metabolism, lipid composition and morphology of different tissues, growth and selected immune parameters, European sea bass juveniles were fed 4 graded levels of CLA (0, 0.5, 1 and 2%). Growth and feed conversion were not affected by CLA, whereas feed intake was reduced (P<0.05) by feeding 2% CLA. In these fish perivisceral fat was also reduced (P<0.05), particularly reducing (P<0.05) monounsaturated fatty acids. CLA has not affected tissue proximal composition, but reduced (P<0.05) saturated and monounsaturated fatty acids and increased (P<0.05) the n-3 and n-3 highly unsaturated fatty acids in muscle and increase (P<0.05) CLA content in muscle, liver and perivisceral fat. A progressive reduction in lipid vacuolization of hepatocytes cytoplasm and regular-shaped morphology was found in fish fed increased CLA levels, together with a progressive increase in malic enzyme activity (only significant in fish fed 1% CLA). Finally, inclusion of CLA up to 1% increased (P<0.05) plasma lysozyme activity and was positively correlated with alternative complement pathway.