Effects of different dietary soybean oil levels on growth, lipid deposition, tissues fatty acid composition and hepatic lipid metabolism related gene expressions in blunt snout bream (Megalobrama amblycephala) juvenile

The present study was conducted to evaluated the effects of different dietary soybean oil (SO) levels on growth performance, lipid deposition, tissues fatty acid compositions and hepatic lipid metabolism related gene expressions in blunt snout bream (M. amblycephala). Fish (average weight 0.34 ± 0.01 g) were fed five experimental diets containing the following inclusion levels of SO: 0% (0%SO), 20% (20%SO), 32% (32%SO), 56% (56%SO) and 100% (100%SO) in dietary lipid, and a diet contained 100% fish oil (100%FO) was also used here. The percentages of 18:2n − 6 in the liver and muscle significantly increased with increasing dietary SO level, and the fish fed 56%SO and 100%SO diets significantly increased 20:4n − 6 contents in the liver and muscle, suggesting blunt snout bream has the capacity to convert C18 fatty acids (PUFAs) to C20/22 fatty acids. However, increasing dietary SO level up-regulated acyl-CoA delta-9 desaturase and down-regulated peroxisome proliferator-activated receptors-α and -β, which might be related associated with high level of 18:2n − 6 in SO. It suggested that supplementation of 20% soybean oil (8% lipid in diet) could improve growth of blunt snout bream juvenile. However, an excess of 18:2n − 6 in SO would modify the expressions of lipid metabolism-related genes, which induced lipid deposition in fish.