EFFECTS OF DIETARY CARBOHYDRATE ON GROWTH PERFORMANCE AND GLYCOMETABOLISM OF LARGE YELLOW CROAKER LARIMICHTHYS CROCEA

To evaluate the effects of dietary carbohydrate on growth performance, feed utilization, plasma parameters, and glycometabolism enzyme activities of large yellow croaker Larimichthys crocea, triplicate groups of fishthe initial body weight:(137.5±0.35) g were randomly fed six isonitrogenous (45% crude protein) and isoenergetic (18 kJ/g gross energy) diets containing graded levels of carbohydrate (1.75%, 6.67%, 13.64%, 21.15%, 26.69% and 32.25%) in floating sea cages for an 8-week feeding trial. Results showed that the highest specific growth rate (SGR) was by 26.69% of dietary carbohydrate. The highest dietary carbohydrate content (32.25%) significantly decreased the SGR (P < 0.05). Both feed efficiency ratio (FER) and protein efficiency ratio (PER) of large yellow croaker fed diets with 13.64% and 21.15% of carbohydrate were significantly higher than those of other groups (P < 0.05). The whole-body lipid content significantly decreased the increased dietary carbohydrate contents with the lowest lipid content 32.25% of carbohydrate group (P < 0.05). Hepatosomatic index (HSI) and liver glycogen content significantly increased with the increased dietary carbohydrate contents (P < 0.05). Plasma total cholesterol and triglyceride levels significantly decreased with the increased dietary carbohydrate level (P < 0.05), but plasma glucose did not impact by dietary carbohydrate level (P>0.05). The increased dietary carbohydrate significantly depressed activities of serum lysozyme, lipoprotein lipase and hepatic lipase (P < 0.05). The activities of intestinal tract amylase and hepatic hexokinase (HK) increased signifi-cantly and then decreased with the highest value at 26.69% and 21.15% dietary carbohydrate contents, respectively (P < 0.05). Dietary carbohydrate significantly up-regulated activities of pyruvate kinase (PK) with the peak level by 32.25% carbohydrate group (P < 0.05). These results indicated the requirement of dietary carbohydrate for large yellow croaker was 22.7%.