The effect of digestible lysine levels was evaluated in diets for Nile tilapia fingerlings (Oreochromis niloticus), Thailand lineage, based on the ideal protein concept. Four hundred and thirty two Nile tilapia fingerlings with an initial body weight of 0.98 ± 0.03 g were allotted in a randomized complete design, with six treatments, six replications per treatment and twelve fish per experimental unit. The treatments consisted of six isoenergetic (3.000 kcal of DE/kg feed) and isoproteic (39.14% CP) diets with different levels of digestible lysine (1.50, 1.66, 1.82, 1.98, 2.14 and 2.30%). Feed intake, digestible lysine intake, average weight gain, specific growth rate, survival rate, feed conversion, daily protein deposition rate, daily fat deposition rate, chemical body composition (moisture, protein and fat content) and nitrogen retention efficiency were evaluated. The different levels of lysine improved linearly the parameters of digestible lysine intake, feed conversion, body protein content and body protein deposition. The Linear Response Plateau model best fitted the parameters of feed consumption, average weight gain, specific growth rate and nitrogen retention efficiency, estimating at 2.06%, 2.17, 2.14 and 2.12% respectively, the level of digestible lysine to maximize each of the parameters. The digestible and total digestible lysine requirement for Nile tilapia fingerlings was 2.17% (0.723%/Mcal of DE) and 2.32% (0.773%/Mcal of DE), respectively, to meet the main performance parameters and carcass traits, when the ideal protein concept was used in diet formulation.
aminoacids; ideal protein; Oreochromis niloticus; proteic nutrition
