Estimating maintenance amino acids requirements of fish through a nonlinear mixed modelling approach

Accurate estimates of maintenance requirement of amino acids are important for feed formulation. However, very little is known about maintenance requirements of essential amino acids in fish. A nonlinear mixed modelling approach was employed in this study to estimate maintenance requirements of essential amino acids of fish from published studies. The maintenance requirements of arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine were estimated to be 7.7 (±6.6), 9.8 (±2.4), 6.4 (±24.8), 9.1 (±13.7), 15.6 (±8.2), 18.4 (±1.9), 14.6 (±3.2), 5.4 (±4.4), 0.5 (±1.3) and 9.3 (±26.6) mg/kg BW^0.75/day respectively, whereas the maintenance requirements of these amino acids as a proportion of their total requirements for protein deposition were estimated to be 4.8%, 31.0%, 8.9%, 12.7%, 5.2%, 11.9%, 19.2%, 2.5%, 2.2%, 10.8% respectively. For most of the essential amino acids, the maintenance requirements represent a small proportion of total requirement (below 10%) with notable exceptions for histidine and phenylalanine. Results from this study suggest that maintenance requirements of fish cannot be assumed equal for all amino acids. The results can be used in developing factorial or mechanistic models of amino acid requirement and utilization.