EFFECTS OF DIETARY CARBOHYDRATE LEVEL ON GLYCOLYTIC ENZYMES AND SERUM GLUCOSE CONCENTRATIONS IN THE JUVENILE SOUTHERN CATFISH AFTER FEEDING

Three isoenergetic diets containing 0%,15% and 30% gelatinized corn starch were formulated as control, middle level and high level carbohydrate(CHO) diets, respectively. The juvenile southern catfish,Silurus meridionalis Chen(50.5±0.6g)were acclimated with control diet for 15d at 27.5±0.5℃. Activities of glycolytic key enzymes(HK, GKand PFK21) and the serum glucose concentrations in the southern catfish respectively fed with the three diets were examined, at 3,6,12,24 and 48h after feeding. The results showed that HKactivity in the middle and high CHO groups were significantly higher than that in the control group(P<0.05)at 24h,but no significant difference was found at other time; GK activity was related positively with CHO level, and the absolute measurement of its activity was much lower than that of HK;PFK21 activity was not significantly different among the three treatments at each measuring time. The results suggested that the glucose phosphorylation in the fish is catalyzed mainly by HK, but its activity could not be significantly induced by dietary CHO level; GKactivity was induced by dietary CHO level so that glucose phosphorylation was promoted, but efficiency of the promotion was not more than 30%. In addition, activity of PFK21 which would catalyze fructose-6-phosphate into fructose 1,6-bisphosphate did not change at different CHO levels, therefore both metabolic mechanisms in glycolysis could not significantly accelerate with the serum glucose concentrations increasing, which might explain the hyperglycemia in the carnivorous fish with nutrition condition of high dietary CHO level.Serum glucose concentration in either the middle or the high CHO groups primarily increased gradually to its peak at 12h after feeding, and then decreased to the basic level, which could provided experimental basis for designing blood sampling time in this kind of research.