Fig. 4. The [5-HIAA]/[5-HT] ratios in the telencephalon (A), hypothalamus (B), optic tectum (C) and brain stem (D) of isolated juvenile rainbow trout fed feeds supplemented with L-tryptophan to a level corresponding to two (2x), four (4x) and eight (8x) times of that of the non-supplemented control feed (1x). Stressed fish (filled squares) were exposed to a standardised stressor (lowering the water level); non-stressed fish were undisturbed fish kept isolated (open triangle). Different letters indicate a significant difference at the P<0.05 level (LSD post-hoc test). Values are means ± S.E.M. from 5-7 individuals.