INFLUENCE OF THE RELATIVE PROPORTIONS OF ENERGY YIELDING NUTRIENTS ONLIVER INTERMEDIARY METABOLISM OF THE EUROPEAN EEL

The influence of dietary protein, lipid and carbohydrate proportions o n liver glutamate dehydrogenase (GDH), fructose 1,6-bisphosphatase (FB Pase), glucose-6-phosphate dehydrogenase (G6PDH) and pyruvate kinase ( PK) activities was investigated in the European eel (Anguilla anguilla ). The highest weight-gain (%) and feed-efficiency indices were obtain ed using diets with the highest energy content and, for the same energ etic content, those with the greatest carbohydrate level. GDH activity increased in fish fed diets with the highest protein:energy ratio wit h respect to diets either with lower protein or with higher total ener gy contents. FBPase showed an increased activity in the liver of fish fed on diets with the lowest carbohydrate content and the highest tota l lipids concentrations. G6PDH activity correlated positively with die tary carbohydrate concentrations and negatively with dietary lipids le vels. The increase of carbohydrates and energy levels in the diet incr eased liver PK activity. In general terms, the European eel showed a c ertain capacity to adapt intermediary metabolism to changes in diet co mposition. Amino acid catabolism increased in response to a higher die tary protein:energy ratio. High carbohydrate levels enhanced glucose u tilization to yield energy and lipid formation. Gluconeogenesis increa sed in response to a lower dietary carbohydrate content. High dietary lipid concentrations reduced gluconeogenesis and lipogenesis from carb ohydrates.