title: Suppression of aggression in rainbow trout (Oncorhynchus mykiss) by dietary L-tryptophan.
abstract: 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.
authors.affiliation: Evolutionary Biology Centre, Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-752 36, Sweden. Svante.Winberg@ebc.uu.se
authors.forename: S
authors.initials: S
authors.lastname: Winberg
authors.forename: Ø
authors.initials: Ø
authors.lastname: Øverli
authors.forename: O
authors.initials: O
authors.lastname: Lepage
mesh_terms: D000374:Aggression / Q000187:drug effects*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001923:Brain Chemistry; D004032:Diet; D004435:Eating; D006854:Hydrocortisone / Q000097:blood; D006897:Hydroxyindoleacetic Acid / Q000032:analysis; D017686:Oncorhynchus mykiss / Q000502:physiology*; D012701:Serotonin / Q000032:analysis; D014364:Tryptophan / Q000008:administration & dosage* / Q000032:analysis / Q000097:blood
chemical_list: D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan; D006854:Hydrocortisone