Fig. 7. The [MHPG] in (A) the optic tectum and (B) brain stem of isolated juvenile rainbow trout fed for 3, 7 or 28 days with a feed supplemented with L-tryptophan (TRP feed) to a level eight times the TRP content of the non-supplemented control feed (CTRL). Stressed fish were exposed to a standardised stressor, a lowering of the water level, whereas non-stressed fish were kept undisturbed. Results (F- and P-values) from a 2-way ANOVA with treatment (stress or no stress) and feed (CTRL or TRP feed for 3, 7 or 28 days) as class variables are given in the figure. Different superscript letters indicate significant differences at the level of P<0.05 (LSD post-hoc test) between the groups. Values are mean ± S.E.M.; for fish fed CTRL feed, N=24; for fish fed TRP feed for 3, 7 and 28 days, N=8.