First published online September 9, 2003
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 Winberg1,*
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
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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© The Company of Biologists Ltd 2003
