Abstract
Fish adjust the enzyme profile to dietary protein and carbohydrate. A balance of nutrients optimizes the enzyme profile and metabolic performance offish. Dietary levels (10, 20, 30 and 40%) were combined to four levels of starch (57, 32, 21 and 4%) to feed juvenile pacu, Piaractus mesopotamicus. Acid and alkaline proteases were color-imetrically determined by hemoglobin and azocasein hydrolysis, respectively. Liver, white and red muscle glycogen, glucose and free amino acids were colorimetrically quantified. Those enzyme activities were induced by dietary protein. Enzyme responses to the feeding and the metabolic profile of the tissues suggest the best protein/starch ratio as 30%/21%. The highest levels of protein (30%-40%) impaired nutrient uptake.