Effects of dietary carbohydrate levels on growth, body composition, and gene expression of key enzymes involved in hepatopancreas metabolism in mud crab Scylla paramamosain

This study estimated the effects of different dietary carbohydrate levels on growth performance, feed utilization, body composition, and the gene expression of key enzymes involved in hepatopancreas lipogenesis and glucose metabolism in mud crab Scylla paramamosain . Crabs with an initial mean weight of 1.84 ± 0.06 g were used in an 8-week experiment to test five diets (C6, C12, C18, C24, C30) formulated to contain increasing levels of carbohydrate, measured as 8.55%, 13.36%, 17.76%, 25.64% and 32.50%, respectively. The results showed that the levels 25.64% and 32.50% improved growth performance, with the best gains at 25.64%. The highest dietary carbohydrate level led to higher hemolymph glucose concentrations and more fat deposition in the body. Furthermore, real-time quantitative PCR analysis revealed that the mRNA expression of key enzymes in glycolytic and lipogenic metabolism (i.e. glucokinase , fructose-2,6-diphosphatase, and fatty acid synthetase) were significantly affected by the dietary carbohydrate level. The mRNA expression of glucokinase was lowest in the group fed the carbohydrate-rich C30 diet, and the mRNA of fructose-2 and 6-diphosphatase were remarkably expressed in the C24 group ( P  < .05). The mRNA expression of fatty acid synthase at the dietary carbohydrate levels 32.50% and 25.64% were respectively 10-fold and 5-fold greater than with 8.55% dietary carbohydrate. The overall data suggest that S. paramamosain can be fed 25.64%–32.50% carbohydrate to achieve satisfactory growth performance. A two-slope broken-line regression analysis of weight gain showed that 24.08% dietary carbohydrate would be optimal for this species reared under similar conditions.