Comparative studies on endocrine status and gene expression of hepatic carbohydrate metabolic enzymes in juvenile GIFT tilapia (Oreochromis niloticus) fed high-carbohydrate diets

Abstract

The effects of high-carbohydrate diets on endocrine status and gene expression of hepatic metabolism enzymes in genetically improved farmed tilapia (GIFT) juveniles (Oreochromis niloticus) at different sampling times were investigated. Two isonitrogenous (28% crude protein) and isolipidic (5% crude lipid) diets were formulated to contain 40% gelatinized wheat starch (WS) or glucose (GLU). Diets were assigned to triplicate groups of 30 fish (initial weight: 51 g) for 42 days. At the end of the trial, there were no significant difference in growth between WS group and GLU group. Hepatosomatic and visceral index and liver glycogen in juveniles were not significantly influenced by high-carbohydrate diets on Day 42 (P > 0.05). Plasma glucose was higher in the GLU group than the WS group from Day 7 onwards. Data on gene expression showed that G6PD, but not GK and G6Pase, were affected by high-carbohydrate diet. The levels of G6PD in the GLU group on Days 35 and 42 were significantly higher than those in the WS group. Serum IGF-I levels of both groups significantly decreased on Day 42, whereas serum insulin levels were unaltered by high-carbohydrate diet. The serum GH level decreased significantly in the GLU group compared with the WS group. Overall, our data suggest that high-glucose diets were efficiently used as an energy source by GIFT tilapia juveniles, and significantly affected liver lipogenic activity and serum GH levels.