Social modulation of sex steroid concentrations in the urine of male cichlid fish Oreochromis mossambicus

Abstract

The relationship between urinary concentrations (free + sulfates + glucuronides) of the steroids testosterone (T), 11-ketotestosterone (11KT), 17α, 20ß-dihydroxy-4-preg- nen-3-one (17,20ß-P) and 17a,20a-dihydroxy-4-preg- nen-3-one (17,20α-P), and the social behavior of males of the cichlid fish Oreochromis mossambicus was inves- tigated. After 8 days of isolation none of the steroids were good predictors 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. Dominance indexes and androgen concentrations mea- sured after all-male group formation were positively cor- related with territoriality, courtship rate, and nest size. Similar relationships were found for progestins with the exception that they were not correlated with courtship rate. All-male group formation was also accompanied by an increase in urinary sex steroid concentrations in fish that became territorial and a decrease in non-territorial fish with the exception of T, which increased in both groups. Addition of ovulating females caused steroid concentrations to return to levels near isolation, except for 17,20α-P in territorials, which underwent a large in- crease. Thus, social interactions may have an important modulatory effect on sex steroid concentrations in O. mossambicus.