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First published online September 9, 2003

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Time-course of the effect of dietary L-tryptophan on plasma cortisol levels in rainbow trout Oncorhynchus mykiss

Olivier Lepage¹, Inmaculada Molina Vílchez¹, Tom G. Pottinger² and Svante Winberg^1,*

¹ Evolutionary Biology Centre, Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36, Sweden
² NERC Centre for Ecology and Hydrology, Windermere Laboratory, The Ferry House, Far Sawrey, Ambleside, Cumbria, UK

View larger version (12K): [in a new window]   Fig. 1. Feed intake, as percentage of body mass, of isolated juvenile rainbow trout after being transferred to observation aquaria. On day 7, the commercial feed was exchanged for a feed supplemented with L-tryptophan to a level eight times (TRP feed) that of the non-supplemented control feed (CTRL feed). Fish were fed to satiation, or to a maximum of 1.5% of the body mass. Values are means ± S.E.M. (days 1-7, N=96; days 8-10, N=48; days 11-17, N=32; days 18-35, N=16).

View larger version (30K): [in a new window]   Fig. 2. Blood plasma levels of (A) cortisol, (B) adrenocorticotropic hormone (ACTH) and (C) L-tryptophan (TRP) in isolated 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 letters indicate significant differences at the P<0.05 level (LSD post-hoc test) between the groups. Different letters above brackets indicate significant differences (P<0.05, LSD post-hoc test) between fish fed control feed and TRP-supplemented feed for 3, 7 and 28 days (stressed and non-stressed fish taken together). Values are means ± S.E.M.; for fish fed CTRL feed, N=24; for fish fed TRP feed for 3, 7 and 28 days, N=8.

View larger version (38K): [in a new window]   Fig. 3. The amount of L-tryptophan (TRP) in (A) the telencephalon, (B) hypothalamus, (C) optic tectum and (D) 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 letters above brackets indicate significant differences (P<0.05, LSD post-hoc test) between fish fed control feed and TRP-supplemented feed for 3, 7 and 28 days (stressed and non-stressed fish taken together). Values are means ± S.E.M.; for fish fed CTRL feed, N=24; for fish fed TRP feed for 3, 7 and 28 days, N=8.

View larger version (37K): [in a new window]   Fig. 4. The [5-HIAA] in (A) the telencephalon, (B) hypothalamus, (C) optic tectum and (D) 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 letters above brackets indicate significant differences (P<0.05, LSD post-hoc test) between fish fed control feed and TRP-supplemented feed for 3, 7 and 28 days (stressed and non-stressed fish taken together). 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.

View larger version (38K): [in a new window]   Fig. 5. The [5-HT] in (A) the telencephalon, (B) hypothalamus, (C) optic tectum and (D) 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 P<0.05 level (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.

View larger version (38K): [in a new window]   Fig. 6. The [5-HIAA]/[5-HT] ratios in (A) the telencephalon, (B) hypothalamus, (C) optic tectum and (D) 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. 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.

View larger version (20K): [in a new window]   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.