RESPONSE OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) TO SUPPLEMENTS OF INDIVIDUAL ESSENTIAL AMINO-ACIDS IN A SEMIPURIFIED DIET, INCLUDING AN ESTIMATE OF THE MAINTENANCE REQUIREMENT FOR ESSENTIAL AMINO-ACIDS

We studied the effects of increasing dietary concentrations of each of the following amino acids on growth, feed intake, feed conversion rat io and composition of gain in rainbow trout in six dose-response exper iments: L-lysine, L-tryptophan, L-histidine, L-valine, L-leucine and L -isoleucine. Semipurified diets containing 20.1 MJ digestible energy/k g dry matter, with wheat gluten and crystalline amino acids as sole so urces of amino acids, were fed to rainbow trout [initial mean body wei ght (BW) 40-51 g, depending on the amino acid studied]. In one series of 24 diets, lysine concentration ranged from 4.5 to 58.0 g/kg dry mat ter; in five further series of 12 diets each, concentrations ranged fr om (in g/kg dry matter): tryptophan, 1.3 to 5.6; histidine, 2.6 to 13. 5; valine, 6.2 to 34.2; leucine, 10.0 to 42.0 and isoleucine, 5.0 to 1 5.3. Each diet was fed to a group of 20 fish for 53-64 d, depending on the amino acid studied. Dry matter intake, weight gain, feed conversi on ratio, protein concentration of gain and total protein deposition f ollowed exponential response functions. To achieve 95% of the maximum protein deposition, dietary concentrations of 27.7 g lysine, 2.0 g try ptophan, 5.8 g histidine, 15.7 g valine, 13.6 g leucine and 13.7 g iso leucine/kg dry matter were required. Maintenance requirements, estimat ed from exponential functions for protein deposition, were [in mg/(100 g BW . d)]: lysine, 1.93; tryptophan, 1.05; histidine, 1.07; valine, 2.92; leucine, 8.26 and isoleucine, 0.91. This corresponds to 4% of th e requirement for protein deposition for lysine and isoleucine but 32% for leucine, with the other amino acids being intermediate. Therefore , different dietary amino acid requirement patterns were derived from protein deposition data depending on the chosen level of performance.