Response of rainbow trout to source and level of supplemental dietary methionine

1. Methionine and total sulfur amino acid (TSAA) requirements of rainbow trout (Salmo gairdneri) were investigated by feeding graded isosulfurous levels of l- and dl-methionine, l-cystine, and the free acid and calcium forms of methionine hydroxy analog (MHA). 2. Added cystine did not promote growth, survival or prevent cataracts. 3. l-methionine produced fastest growth, followed by dl-methionine, CaMHA and free acid MHA. 4. Trout fed CaMHA gained 85.7 and 92.3% as much as those fed l-methionine and dl-methionine. 5. Within each experiment, the level of L-methionine isomer that prevented cataracts was constant (1.86 g/100g protein in experiment (1), 1.45 in experiment (2) and was lower than for maximum growth (2.89 and 2.15 g) regardless of methionine source.