Effects of three different carbohydrate sources on growth performance and hepatic glucose metabolism key enzyme activities in large yellow croaker (Larimichthys crocea)

An 8-week feeding trial and a 24-hour starvation trial were conducted to evaluate the effects of three different carbohydrate sources on growth performance, feed utilization and glucose metabolism key enzyme activities of large yellow croaker. Three isonitrogenous and isoenergetic diets (about 48% crude protein and 12% crude lipid) were formulated to supplement with three different carbohydrate sources, namely glucose, wheat starch and dextrin, respectively. Each diet was randomly assigned to feed three replicate groups of 50 juvenile large yellow croakers with the initial weight of (8.51±0.02) g twice daily to apparent satiation. After the end of the feeding trial, the fish was continuously starved for 24 h and samples were taken at 0, 1, 3, 5, 7, 9, 11, 24 h, respectively. The results indicated that fish fed the diets containing wheat starch and dextrin had significantly higher weight gain rate (WGR) and specific growth rate (SGR) than those fed the diet containing glucose, moreover, feed conversion ratio (FCR) of these two diets was significantly lower than that of diet containing glucose. Fish fed the diet containing dextrin had significantly higher hepatosomatic index (HSI) than those fed the other diets. However, survival rate (SR), viscerosomatic index (VSI) and condition factor (CF) were not significantly affected by three different carbohydrate sources. Serum glucose (GLU) concentration of the diet containing glucose and wheat starch significantly increased after starving 1 h and glucose diet group presented high serum glucose levels which lasted for at least 10 h. However, serum glucose concentration of the diet containing wheat starch significantly decreased to initial level and didn’t display high serum glucose level. Serum glucose concentration of the dextrin diet group continuously increased as time went on, peaked at 11 h, and high serum glucose level lasted for at least 4 h. The concentration of serum insulin and hepatic glycogen were significantly affected by diets supplemented with three different carbohydrates. The results indicated that the increasing of glucokinase (GK) can be induced by wheat starch. While serum glucose concentration increased after feeding trial, the activities of gluconeogenic key enzymes such as glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK) didn’t decrease. The activities of pyruvate kinase (PK) were significantly influenced by the dietary glucose and wheat starch. The results demonstrated that the ability of utilizing structure-complicated polysaccharide (such as wheat starch and dextrin) was higher than that of utilizing monosaccharide (such as glucose). Not only the serum glucose regulation but also the activities of glycolysis and gluconeogenic key enzymes were affected by different dietary carbohydrate sources.