The increasing importance of fish welfare in aquaculture is not only an ethical question but a chance to improve standards and quality of fish production technologies and aquaculture products. Fish kept under good welfare conditions have lower stress levels, are less prone to diseases, have better growth and food conversion rates (FCR) and have a better final flesh quality. T ryptophan is known to be linked to the stress response by enhancing fish brain serotonergic activity and can also inhibit endogenously derived behavioural performance, such as aggressiveness and cannibalism. 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 , the re was a tendency to an increase of growth and decrease of FCR in meagre fed higher levels of tryptophan. This is supported by the results obtained in muscle cellularity where Trip3 had a higher fibre density, suggesting an increased fibre recruitment. In terms of fish behaviour, very little differences were found . In the anxiety test, fish fed the higher quantity of tryptophan showed a significantly lower number of freezing episodes compared to fish fed the lowest tryptophan amount , suggesting more ability to explore and lower levels of anxiety . These results suggest that tryptophan dietary levels can influence not only meagre growth pattern but, as well, its behavioural response.