REGULATION OF CARBOHYDRATE-METABOLISM IN FISH .21. EFFECTS OF DIETARY GLUCOSE, FRUCTOSE, AND GALACTOSE ON HEPATOPANCREATIC ENZYME-ACTIVITIES AND BODY-COMPOSITION IN CARP

In order to investigate the metabolic response to dietary glucose, fructose, and galactose in carp Cyprinus carpio, tolerance tests of these monosaccharides and feeding trials were conducted. After oral administration of 50 mg of glucose, fructose or galactose per 100 g body weight, serum glucose, fructose, and galactose levels increased to the maximum until 1.5 h. Although these sugar level decreased thereafter, the decreases of serum glucose and fructose levels were faster than the decrease of serum galactose levels. In the feeding experiment, carp were fed on a high-protein diet and four diets containing 30% of starch, glucose, fructose, and galactose for 30 days. The fish fed galactose showed a remarkable reduction of growth rate, several body component levels, and hepatopancreatic enzyme activities. Dietary supplementation with starch, glucose or fructose depressed the activities of gluconeogenic and amino acid degrading enzymes and raised the activity of phosphofructokinase. The activities of lipogenic enzymes and the levels of serum lipds were raised by dietary starch and glucose but not by dietary fructose. These results suggest that both glucose and fructose in the diet depress gluconeogenesis and amino acid degradation and accelerate glycolysis, but that fructose, unlike glucose, does not promote lipogenesis in the hepatopancreas of carp.