Effect of Dietary Carbohydrate on Growth, Glucose Tolerance, and Liver Composition of Juvenile Striped Bass

Dietary carbohydrate utilization by juvenile striped bass was evaluated in two studies. An incomplete factorial design was employed to determine the effect of carbohydrate complexity and dietary level on glucose tolerance. Five diets were formulated to contain 0, 12.5, or 25% of glucose or cornstarch, respectively. After 4 weeks, fish were fasted and administered an oral glucose challenge of 167 mg glucose/100 g body weight. Blood samples were collected at 0, 1, 2, 3, 4, 5, and 6 h after administration. Fasting plasma glucose concentrations (7.2 ± 0.8 mM/L) were similar among all treatments. Plasma glucose concentrations peaked higher at 4 and 5 h after administration in fish fed diets containing 25% glucose (23.9 ± 3.6 and 23.3 ± 3.2 mM/L, respectively) and 25% cornstarch (26.1 ± 2.0 and 23.9 ± 4.0 mM/L, respectively) when compared with plasma values for fish fed 0 and 12.5% carbohydrate (P < 0.05). There was neither a significant effect of carbohydrate type nor a significant interaction between type and level (P > 0.05). In the second study, five diets containing 0, 10, 15, 20, and 25% glucose were fed to juvenile striped bass. After 7 weeks, oral administration of glucose resulted in a persistent hyperglycemia. Weight gain and feed efficiency were significantly decreased (P < 0.05) in fish fed dietary glucose at concentrations above 15%. Inclusion of dietary glucose resulted in greater (P < 0.05) hepatosomatic index values and liver glycogen concentration. However there were no significant effects in liver proximate composition (P > 0.05). These data suggest that striped bass are able to most effectively utilize dietary carbohydrate at a maximal level between 15 and 20% of the diet.