Intermale competition in sexually mature arctic charr: Effects on brain monoamines, endocrine stress responses, sex hormone levels, and behavior

Sexually mature Arctic charr (Salvelinus alpinus) males were allowed to int eract in pairs for 4 days in the absence of females. Agonistic behavior was quantified, and at the end of the experiment, plasma levels of glucose, co rtisol, testosterone (T), 11-ketotestosterone (11-KT), and 17 alpha,20 beta -dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P) were determined alongside b rain concentrations of serotonin (5-HT), S-hydroxyindoleacetic acid (5-HIAA , the major 5-HT metabolite), dopamine (DA), and 3,4-dihydroxy-phenylacetic acid (DOPAC, a major DA metabolite). Plasma cortisol and glucose were sign ificantly elevated in subordinate fish, and the number of aggressive acts r eceived showed positive correlations with plasma levels of glucose on day 1 , during the development of the dominance relationship, and of cortisol on day 4, when the dominance relationship was established. In contrast, plasma concentrations of T and 11-KT were significantly higher in dominant than i n subordinate males, and there was a similar tendency in plasma concentrati ons of 17 alpha,20 beta-P. Further, plasma levels of these gonadal steroids were correlated with the number of aggressive acts performed on day 4, but not with the number of aggressive acts received. The plasma cortisol conce ntrations did not correlate with either 5-HIAA:5-HT or DOPAC:DA ratios in a ny of the brain parts analyzed. Plasma glucose levels showed positive corre lations with brain 5-HIAA: S-HT ratios. Negative correlations were observed between S-HIAA:5-HT ratios in the optic tectum and between plasma levels o f T, 11-KT, and 17 alpha,20 beta-P. Telencephalic DOPAC/DA ratios displayed a negative correlation with plasma levels of T, 11-KT, and 17 alpha,20 bet a-P, but only in dominant males. (C) 2000 Academic Press.