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

Soybean oil (SO) is widely used in freshwater aqua-feeds in China. However, little information is available about the effects of dietary SO levels on lipid deposition and hepatic lipid metabolism in fish. This study evaluated 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 (Megalobrama amblycephala). Fish (average weight 0.34±0.01g) were fed five experimental diets containing 0% (0%SO), 20% (20%SO), 32% (32%SO), 56% (56%SO) and 100% (100%SO) SO in dietary lipid, and a diet containing 100% fish oil (100%FO). The body weight gain of fish fed 20%SO and 100%FO diets were significantly higher than in the other groups. Hepatic lipid content increased with incremental dietary SO level. The percentages of 18:2n−6 in the liver and muscle significantly increased with increasing dietary SO level. In the fish fed 56%SO and 100%SO diets 20:4n−6 content significantly increased in the liver and muscle suggesting the capacity of blunt snout bream 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 responsible for the high 18:2n−6 content. It is suggested that supplementation of 20% soybean oil (8% lipid in diet) could improve blunt snout bream juvenile growth. However, an excess of 18:2n−6 in SO supplemented diets modified the expressions of lipid metabolism-related genes which induced lipid deposition.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±0.01g) 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.