AGONISTIC INTERACTIONS AFFECT BRAIN SEROTONERGIC ACTIVITY IN AN ACANTHOPTERYGIIAN FISH - THE BICOLOR DAMSELFISH (POMACENTRUS-PARTITUS)

Bicolor damselfish were allowed to interact in pairs for 15 min a day during a five-day period. Agonistic behaviour was quantified, and at t he end of the experimental series, concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan (TRP, the amino ac id precursor of 5-HT) were measured, and 5-HIAA/5-HT ratios (an index of 5-HT activity) were calculated in the telencephalon, hypothalamus a nd brain stem. Socially interacting fish, dominant as well as subordin ate, showed higher telencephalic 5-HIAA/5-HT ratios than isolated cont rols. Social interaction also decreased telencephalic TRP concentratio ns in subordinate fish but did not affect 5-HT concentrations in any o f the brain parts. In subordinate fish, 5-HIAA/5-HT ratios in the tele ncephalon were positively correlated with the number of aggressive act s received. Moreover, in dominant fish 5-HIAA/5-HT ratios in the hypot halamus were positively correlated with the number of aggressive acts performed. These results indicate that the brain serotonergic system i s involved in intraspecific aggression and/or stress reactions in bico lor damselfish.