Suppression of aggression in rainbow trout (Oncorhynchus mykiss) by dietary L-tryptophan
Svante Winberg1,*,
Øyvind Øverli2 and
Olivier Lepage1
1 Evolutionary Biology Centre, Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36, Sweden and
2 Evolutionary Biology Centre, Department of Animal Development and Genetics, Uppsala University, Norbyvägen 18A, SE-752 36, Sweden
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Fig. 1. The number of aggressive acts performed during repeated 30 min resident/intruder tests by isolated juvenile rainbow trout before (day 0) and after 3 and 7 days of receiving an experimental wet feed supplemented with (A) 1.5 % (experiment 1) or (B) 0.15 % (experiment 2) L-tryptophan (TRP). In both experiments, the control fish were fed experimental wet feed without supplementary tryptophan. Values are means + S.E.M. (N=12 in all groups). *P<0.05 (repeated-measures MANOVA followed by contrast analysis, see text for further details).
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Fig. 2. Attack latency of isolated juvenile rainbow trout in repeated 30 min resident/intruder tests performed before (day 0) and 3 and 7 days after feeding the fish with an experimental wet feed supplemented with (A) 1.5 % (experiment 1) or (B) 0.15 % (experiment 2) L-tryptophan (TRP). In both experiments, the control fish were fed the same experimental wet feed but without supplementary tryptophan. Values are means + S.E.M. (N=12 in all groups).
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Fig. 3. Feed intake, determined as the amount of feed (dry mass) consumed per kilogram of body mass, of isolated juvenile rainbow trout after being transferred to observation aquaria. On day 7, the commercial trout feed was exchanged for an experimental wet feed supplemented with 1.5 % (experiment 1) or 0.15 % (experiment 2) L-tryptophan (TRP). In both experiments, the control fish were fed the same experimental wet feed but without supplementary tryptophan. Feed intake was not registered on day 6. Values are means ± S.E.M.
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Fig. 4. The amount of L-tryptophan (TRP) in the blood plasma, brain stem (BS), hypothalamus (Hyp) and telencephalon (Tel) of isolated juvenile rainbow trout fed an experimental wet feed supplemented with 1.5 % (experiment 1) or 0.15 % (experiment 2) L-tryptophan (TRP) for 7 days. In both experiments, the control fish were fed the same experimental wet feed but without supplementary tryptophan. Intruder-tested fish were subjected to resident/intruder tests (see text for details). Values are means + S.E.M. (intruder-tested, N=10–12; non-tested, N=6–12). ***P<0.001, **P<0.01 (repeated-measures MANOVA followed by contrast analysis, see text for further details).
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Fig. 5. Plasma levels of cortisol in isolated juvenile rainbow trout fed an experimental wet feed supplemented with 1.5 % (experiment 1) or 0.15 % (experiment 2) L-tryptophan (TRP) for 7 days. In both experiments, the control fish were fed the same experimental wet feed but without supplementary tryptophan. Intruder-tested fish were subjected to resident/intruder tests (see text for details). Values are means + S.E.M. (intruder-tested, N=10–12; non-tested, N=6–12).
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Fig. 6. The [5-hydroxyindoleacetic acid]/[serotonin] ([5-HIAA]/[5-HT]) ratios in the brain stem (BS), hypothalamus (Hyp) and telencephalon (Tel) of isolated juvenile rainbow trout fed an experimental wet feed supplemented with 1.5 % (experiment 1) or 0.15 % (experiment 2) L-tryptophan (TRP) for 7 days. In both experiments, the control fish were fed the same experimental wet feed but without supplementary tryptophan. Intruder-tested fish were subjected to resident/intruder tests (see text for details). Values are means + S.E.M. (intruder-tested, N=10–12; non-tested, N=6–12). ***P<0.001, *P<0.05 (repeated-measures MANOVA followed by contrast analysis, see text for further details).
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© The Company of Biologists Ltd 2001
