Effect of corn oil levels on growth, biochemical profiles and expression of FADS2 and ELOVL5 genes in Cyprinus carpio var. communis.

Lipids play significant roles in energy metabolism, nutrient utilization, and the regulation of lipid metabolism in fish and is thus considered as one of the important components of aquafeeds. Common carp, Cyprinus carpio var. communis, is a widely cultured fish species worldwide; however, information on the optimum corn oil inclusion level under defined dietary formulations remains limited. Therefore, this study evaluated the effects of graded corn oil inclusion levels on growth performance, serum biochemical profile, haematological parameters, digestive enzyme activities, and mRNA expression of fatty acid desaturase 2 (FADS2) and elongation of very long-chain fatty acids protein 5 (ELOVL5) in common carp fingerlings (1.59 ± 0.02 g/fish) over a 10-week feeding trial. Fish were fed six isonitrogenous diets containing graded levels of corn oil (20-120 g k1) with a constant inclusion of 20 g kg-1 cod liver oil. Growth performance improved significantly (P < 0.05) with increasing corn oil inclusion up to 60 g kg-1 and declined thereafter. Whole-body protein, fat, and moisture contents were significantly affected, whereas body ash content remained unchanged. Fish fed the diet containing 60 g kg-1 corn oil exhibited improved haematological indices, enhanced protease and lipase activities, and higher relative expression of FADS2 and ELOVL5. Quadratic regression analyses based on live weight gain (LWG), feed conversion ratio (FCR), and body protein deposition (BPD) estimated an optimum corn oil inclusion level of 68.60 g kg-1 in the presence of 20 g kg-1 cod liver oil in the feed under the present experimental conditions. These findings indicate that moderate corn oil inclusion under the present dietary formulation was associated with improved growth performance, physiological responses, digestive enzyme activities, and FADS2 and ELOVL5 expression in common carp fingerlings.