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¹ Shanghai Ocean University, Key Laboratory of Freshwater Fishery Germplasm Resources, Ministry of Agriculture, P. R. China DOI : 10.4194/1303-2712-v17_2_20 Viewed : 5324 - Downloaded : 4522 This study was aimed at elucidating the effects of replacing fish oil (FO) with palm oil (PO) on tissue fatty acid composition, lipogenic enzyme activities and mRNA expression of genes related to lipid metabolism in Nile tilapia, Oreochromis niloticus (6.72± 0.14g). An eight week feeding trial was conducted using five isonitrogenous and isolipidic diets containing 0% PO, 25% PO, 50% PO, 75% PO and 100% PO. PO supplementation led to a significant increase in total saturated fatty acid (SFA), total mono unsaturated fatty acids (MUFA) and 18: 2n-6, whiles DHA, EPA, total n-3 as well as 20: 2n-6 were reduced significantly in the liver (P＜0.05). With the exception of glycerol-3-phosphate acyltransferase (GPAT) enzyme activity, supplementing tilapia diet with PO significantly increased fatty acid synthesase (FAS), acetyl-CoA carboxylase (ACC), steroyl-CoA desaturase 1 (SCD1), ATP citrate lyase (ACYL), carnitine palmitoyltransferase Ia (CPTIa) and carnitine palmitoyltransferase Ib (CPT Ib) (P＜0.05). In addition, significant/positive correlations were observed among dietary PO and/or liver tissue FA with FAS, ACC, SCD1 and ACYL mRNA expression while a negative correlation was recorded for CPTI mRNA expression. Generally, inclusion of PO in tilapia diets resulted in lipid accumulation in the liver and altered the key gene expression of lipid metabolism. Keywords : Stearoyl-CoA desaturate 1, Fatty acid synthesase, Carnitine palmitoyltransferase (CPT) I, Acetyl-CoA Carboxylase, ATP Citrate Lyase, Lipid metabolism, Oreochromis niloticus, Palm oil