Effects of dietary carbohydrate levels on growth, glucose tolerance, glucose homeostasis and GLUT4 gene expression inTilapia nilotica

In this paper, the glucose tolerance tests (GTT) were performed to evaluate the effects of three dietary carbohydrate levels on growth, plasma glucose, hormones (insulin and IGF-I), glucose homeostasis and GLUT4 gene expression of Tilapia nilotica. Juvenile tilapia (av. wt.10 g) were randomly distributed into three groups with three replicates and fed for 8 weeks with three dietary carbohydrate levels: 40% (CH), 30% (CM) and 20% (CL). After 8 weeks of feeding trial, fish were injected with glucose (30 mg/100 g body weight) for GTT. The growth performance results showed the survival rate in the CH group was significantly lower than the other two groups (p < 0.05). The GTT results showed that the plasma glucose level positively correlates with the diets' carbohydrate level initially, peaked at 1 hr and declined thereafter. The plasma IGF-1 levels were positively correlated with diets' carbohydrate levels; first the levels increase and then decrease after injection in all the three groups. There was a direct relationship between the carbohydrate levels and the activities of liver pyruvate kinase (PK) and glucokinase (GK) enzymes. Muscle GLUT4 expression in groups changed slightly in 0–3 hr and then increased sharply during 6–12 hr. Results of this study indicated that the moderate dietary carbohydrate level may improve the glucose tolerance of T. nilotica. The carbohydrate levels can affect plasma glucose, IGF-1 and GLUT4 expression in T. nilotica. In addition, the IGF-1 may play a more important role on the glucose metabolism than insulin. The delayed gene transcription of GLUT4 may be one of the reasons for glucose intolerance in T. nilotica.