Abstract:
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%.