Dietary cholesterol promotes the growth of mud crabs, Scylla paramamosain by regulating cholesterol metabolism, enhancing ecdysteroid synthesis and molting cascade response

A seven-week feeding trial was conducted to evaluate the effects of dietary cholesterol on growth, proximate composition, cholesterol metabolism, ecdysteroids synthesis and molting cascade response in mud crab (Scylla paramamosain). Six isonitrogenous and isolipidic diets (46 % protein and 11 % lipid) were formulated to contain graded levels of cholesterol, with the analyzed levels of cholesterol being 0.15 %, 0.32 %, 0.54 %, 0.72 %, 0.91 % and 1.53 %, respectively. A total of 180 crabs (initial weight 16.26 ± 0.02 g) were separated into six treatments, each treatment dividing randomly into three replicates of 10 crabs. The results showed that crabs fed the diets with 0.54 %-0.91 % cholesterol displayed significantly higher FW, PWG, SGR and FE than those fed the diet with 0.15 % cholesterol. The hepatopancreas lipid content of the crabs with dietary 1.53 % cholesterol was significantly higher than that of the crabs without dietary cholesterol supplementation. Compared to crabs fed the diet with 0.15 % cholesterol, significantly higher concentrations of ApoA, HDL-C, LDL-C, VLDL-C in serum and ApoA, HDL-C in hepatopancreas were observed at crabs fed the diet with 0.72 % cholesterol. The highest concentrations of 20E and MF in serum were observed at crabs fed the diet with 0.72 % cholesterol, whereas the concentration of MIH in serum was significantly lower in crabs fed the diets with 0.72 % and 0.91 % cholesterol than those fed the diets with 0.15 % and 1.53 % cholesterol. The expression levels of genes related to cholesterol metabolism (srb, ldlr, lrp2, cyp27a1 and start3) in hepatopancreas were significantly higher in crabs fed the diet with 0.54 % cholesterol than those fed the diet with 0.15 % cholesterol. The expression levels of molting-related genes (nvd, dib, rxr, br-c, e74b, e75, ftz-f1, met) were significantly higher in crabs fed the diet with 0.54 % cholesterol than crabs fed the diet with 1.53 % cholesterol. The highest expression level of ecr was in 0.72 % and 0.91 % cholesterol group. With dietary cholesterol increasing from 0.15 % to 1.53 %, the expression levels of mfe and jheh significantly decreased, whereas the expression levels of famet and hr38 significantly increased. In conclusion, 0.54 %-0.72 % cholesterol promoted cholesterol metabolism and activated expression levels of molting-related genes, leading the better growth performance of mud crabs. Based on PWG and the R-Square (R²) of the equations, two equations of the linear truncated model (Y = 45.98X + 57.562 and Y = − 33.312X + 112.31) were used to calculate the optimal cholesterol requirement of 0.68 % for juvenile mud crabs.