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The Journal of Experimental Biology 204, 3867-3876 (2001)
© 2001 The Company of Biologists Limited

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

*e-mail: Svante.Winberg{at}ebc.uu.se

Accepted August 20, 2001

Juvenile rainbow trout Oncorhynchus mykiss were isolated in individual compartments in observation aquaria and allowed to acclimate for 1 week, during which they were fed commercial trout feed. Thereafter, the fish were tested for aggressive behaviour using a resident/intruder test. Following this first resident/intruder test, the feed was exchanged for an experimental wet feed supplemented with 0.15 % or 1.5 % L-tryptophan (by wet mass). Controls received the same feed but without L-tryptophan supplementation. The fish were fed to satiety daily, and their individual feed intake was recorded. Aggressive behaviour was quantified again after 3 and 7 days of L-tryptophan feeding using the resident/intruder test. Feeding the fish L-tryptophan-supplemented feed for 3 days had no effect on aggressive behaviour, whereas feeding the fish L-tryptophan-supplemented feed for 7 days significantly suppressed aggressive behaviour in the fish, an effect seen at both levels of L-tryptophan supplementation. Fish fed L-tryptophan-supplemented feed showed elevated plasma and brain levels of L-tryptophan. The amino acid L-tryptophan is the precursor of serotonin, and supplementary dietary L-tryptophan was found to elevate levels of 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HIAA/serotonin concentration ratio in the brain. Neither feed intake nor plasma cortisol level was significantly affected by dietary L-tryptophan. Central serotonin is believed to have an inhibitory effect on aggressive behaviour, and it is suggested that the suppressive effect of dietary L-tryptophan on aggressive behaviour is mediated by an elevation of brain serotonergic activity.

Key words: serotonin, brain, behaviour, fish, feed, stress, Salmonidae, Oncorhynchus mykiss.




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O. Lepage, O. Tottmar, and S. Winberg
Elevated dietary intake of L-tryptophan counteracts the stress-induced elevation of plasma cortisol in rainbow trout (Oncorhynchus mykiss)
J. Exp. Biol., December 1, 2002; 205(23): 3679 - 3687.
[Abstract] [Full Text] [PDF]


© The Company of Biologists Ltd 2001