The objective of this study was to determine the coefficients of apparent and true digestibility of protein and amino acids of five feedstuffs (corn, wheat bran, soybean meal, corn gluten meal and fish meal) in 900 sex-reversed Nile tilapia (Oreochromis niloticus) of the Thai strain during the growth phase, with an initial weight of 315±8.45 g. A total of 750 fish were distributed according to a randomized block design (repetitions in time) into five treatments with six replicates of 25 fish each. The remaining 150 fish were fed a protein-free diet to measure endogenous protein and amino acid losses in order to determine the true digestibility of these components. Each tested diet contained a single protein source, which consisted of one of the evaluated feedstuffs. Digestibility was indirectly estimated using chromic oxide at 0.50% as marker. Digesta was collected from the last 5 cm of the distal intestine (between the ileal-rectal valve and the anus) using the dissection technique. Apparent digestibility coefficients of protein and amino acids were, on average, 74.69 and 73.62% for corn, 73.74 and 72.81% for wheat bran, 86.01 and 84.66% for soybean meal, 85.19 and 84.29% for corn gluten meal, 76.74 and 75.56% for fish meal, respectively. True digestibility coefficients of protein and amino acids were, on average, 85.21 and 83.97% for corn, 84.41 and 83.74% for wheat bran, 87.22 and 87.51% for soybean meal, 87.97 and 87.34% for corn gluten meal, and finally 79.58 and 78.44% for fish meal, respectively.
digestible amino acids; endogenous loss; protein-free diet; Oreochromis niloticus
