Effects of diet on lipogenic enzyme activities in channel catfish hepatic and adipose tissue

Three isonitrogenous, isoenergetic diets were formulated with varying levels of carbohydrate (CHO) and lipid to determine the effect of energy source on lipogenic enzyme activities in fingerling channel catfish. Diets A, B, and C contained, expressed as a percentage of total energy, 0% CHO and 49% lipid, 16% CHO and 33% lipid, and 46% CHO and 3% lipid, respectively. Duplicate groups of 60 fish weighing 435 +/- 5 g/group were fed 3% of their wet weight per day. Fish fed the high lipid (A) diet grew as well as fish fed the high-CHO (C) diet. Fish fed diet B, however, had a significantly greater growth rate. Fish were sampled and composite samples of liver and mesenteric adipose tissue were assayed for the following enzymes: fatty acid synthetase, malic enzyme, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and NADP-isocitrate dehydrogenase. In both hepatic and adipose tissue, all lipogenic enzymes assayed were stimulated by the high-CHO diet. All lipogenic enzymes were depressed by the high lipid diet only in hepatic tissue. Enzyme activities were much lower in adipose tissue relative to hepatic tissue. The marked stimulation of the hepatic lipogenic enzyme activities by dietary CHO may explain why catfish can utilize higher levels of dietary CHO than certain solmonid fishes.