Tryptophan has been shown to affect fish feed intake and growth performance. Moreover, is the precursor of several bioactive molecules such as serotonin, which can be converted into melatonin. Melatonin is a potent antioxidant that directly neutralizes free radicals and reduces oxidative stress. Diets rich in tryptophan can lead to lower free radical production due to the calming effect of serotonin and the antioxidant effect of melatonin. In this study, three diets containing different contents of tryptophan: 0.5 (Trip1), 0.7 (Trip2) and 0.8 % (Trip3), were tested in triplicates in 112 days old meagre with an initial weight of 32.6 ± 3.4 g and 14.4 ± 0.5 cm length for 57 days. Although the results showed no significant differences for growth and FCR between treatments, there was a tendency to an increase of growth and decrease of FCR in meagre fed higher levels of tryptophan. However, the main protein degradation systems in the liver and white muscle showed that the activity of the tested proteases in the muscle were unaffected by the levels of dietary tryptophan. A decrease in oxidative stress was also observed as the level of tryptophan in the diets increased, although not statistically significant. A trend of decreasing superoxide dismutase, catalase and selenium-independent glutathione peroxidase levels in tryptophan-rich diets were also observed.