The capacity of carbohydrate digestion and metabolism is generally poor in fishes. A large number of studies have showed that high dietary carbohydrate intakes result in persistent hyperglycemiaand reduced growth rate and feed utilization. A lot of factors influence carbohydrate utilization of fishesdevelopment stageenzymes of carbohydrate digestion and metabolismas well as type and content of dietary carbohydrateand water temperature. This review examines some of the background and the possible mechanistic bases for carbohydrate utilization in fish regarding to energy metabolism. We propose that the poor carbohydrate utilization of fishes would be due to their relative low level of energy metabolism. Since the rate of energy consumption is low in fish while the rate of energy supply is high with carbohydrate as fuelthe rate of energy supply might be overabundance after excess carbohydrate intakewhich results in persistent hyperglycemia. The influence of carbohydrate typeand water temperature on utilization of dietary carbohydrate in fish might also be related to this potential mechanism