Modeling lysine requirements of Oreochromis niloticus due to principles of the diet dilution technique

Two experiments were conducted using 16 mixed diets with lysine as the first limiting dietary amino acid. Experimental diets were randomly assigned to four replicate tanks with 25 fish per tank (experiment I) or 18 fish per tank (experiment II) and fed to juvenile all male Nile tilapia for 56 days (12.0 g average body weight at start). Protein deposition depending on the intake of the limiting amino acid was measured by total body analysis of 10 fish per experiment at the beginning and 3 fish per replicate tank at the end of the study. N-deposition data were statistically analyzed using a non-linear N-utilization model for assessment of the dietary efficiency of lysine utilization. Results were evaluated to provide reliable information about dietary lysine efficiency and approved data were utilized for model calculation of lysine requirements. Using predicted daily feed intake (3 vs. 2.5%) and dietary lysine efficiency as measured, the optimal dietary lysine concentration was calculated corresponding to 60% (1.29 vs. 1.55% lysine), 70% (1.63 vs. 1.95% lysine), and 80% (2.09 vs. 2.51% lysine) of the genetic potential for nitrogen deposition (NDmaxT). The observed lysine requirements for growth performance between 60 and 70% of NDmaxT were in line with actual recommendations. Additionally, the delivered effect of varying dietary efficiency of lysine utilization on calculated lysine requirements ranks this factor as very important and needs more experiments for reliable evaluation of variation of lysine efficiency in practical fish diets. Before application of the established lysine requirement data in diet formulation, more experimental data due to this important dietary factor of influence are needed.