Amino acid requirement studies in Oreochromis niloticus by application of principles of the diet dilution technique

Data analysis utilized four growth experiments with mixed diets limiting in lysine, in threonine, and in methionine respectively. All male juvenile Orechromis niloticus [12 g average body weight instead of average (BW) at start, four repetition tanks per diet, 56 days experimental period] provided the database for application of an exponential N-utilization model. Imposing amino acid efficiency data were utilized for modelling of amino acid requirements depending on the level of daily protein deposition. According to the observed average dietary amino acid efficiency of the amino acids under study, 16.3 g/kg of lysine, 8.3 g/kg of threonine and 7.3 g/kg of methionine were established as required in feed content for 187 mg daily protein deposition (50 g BW, feed intake at 3% of BW). Further modelling by use of graded dietary amino acid efficiency yielded strong evidence for the significance of this dietary factor of influence. Current data analysis has led to conclusion, that the applied non-linear modelling of amino acid requirements is an advantageous approach because of its quantitative reflection of graded dietary amino acid efficiency corresponding to protein deposition data. The procedure has the potential to contribute to alternate approaches for improved reliability of recommended quantitative amino acid supply in fish nutrition.