Utilization of glucose, maltose, dextrin and cellulose by juvenile flounder (Paralichthys olivaceus)

Abstract

A study was conducted to determine the ability of juvenile flounder to utilize different sources of carbohydrate in their diets. Triplicate groups of fish (average weight, 4 g) were hand-fed visual satiety one of seven diets containing 15% cellulose, 15% glucose, 15% maltose, and 5–25% dextrin for 45 days in flush-out aquarium system. Weight gain, feed efficiency ratio, protein efficiency ratio (PER), energy retention efficiency, hepatosomatic index (HSI), and liver glycogen were measured. Fish fed the diet containing 15% cellulose had the lowest weight gain (P<0.05) among all groups. Weight gain of fish fed the diets containing 15% maltose and 15–25% dextrin was higher than that of fish fed the diets containing 15% cellulose and 5% dextrin. The feed efficiency ratio and PER of fish fed the diets containing 15–25% dextrin were significantly higher (P<0.05) than those of the other groups. Growth and feed utilization increased with an increase in the dextrin level of the diet. Lipid content of the whole body and liver decreased with an increase in dietary dextrin level. Liver glycogen and HSI of fish fed the 15% glucose and 15% maltose diets were higher (P<0.05) than those of fish fed the other carbohydrates, however these values were not affected by an increase in dextrin intake. Flounder (average weight, 15 g) were fasted for 48 h for a glucose tolerance test and blood was collected after feeding at 0, 1, 3, 5, 8, 11, 16, 24 and 48 h. Plasma glucose concentrations of fish fed the diets containing 15% glucose and 15% maltose peaked at 5–8 h (200 mg/100 ml) and 5 h (148 mg/100 ml), respectively, then decreased at 24 and 16 h. Fish fed the diets containing 5–25% dextrin showed a lower glucose level (87–97 mg/100 ml) than fish fed the other diets and it peaked between 3 and 5 h. Flounder utilized dextrin more efficiently than glucose, and dextrin was a better source of energy than lipid. The best growth and feed utilization were achieved with the diet containing 25% dextrin and 6% lipid.