SOCIAL MODULATION OF SEX STEROID CONCENTRATIONS IN THE URINE OF MALE CICHLID FISH OREOCHROMIS-MOSSAMBICUS

The relationship between urinary concentrations (free + sulfates + glu curonides) of the steroids testosterone (T), 11-ketotestosterone (11 K T), 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 alpha-P), and the socia l behavior of males of the cichlid fish Oreochromis mossambicus was in vestigated. After 8 days of isolation none of the steroids were good p redictors of social dominance developed after subsequent formation of all-male groups. One day after group formation dominance indexes were good predictors of the urine concentrations of all sex steroids. Domin ance indexes and androgen concentrations measured after all-male group formation were positively correlated with territoriality, courtship r ate, and nest size. Similar relationships were found for progestins wi th the exception that they were not correlated with courtship rate. Al l-male group formation was also accompanied by an increase in urinary sex steroid concentrations in fish that became territorial and a decre ase in non-territorial fish with the exception of T, which increased i n both groups. Addition of ovulating females caused steroid concentrat ions to return to levels near isolation, except for 17,20 alpha-P in t erritorials, which underwent a large increase. Thus, social interactio ns may have an important modulatory effect on sex steroid concentratio ns in O. mossambicus. (C) 1996 Academic Press, Inc.