Steroids in the control of reproductive function in fish.

Serum and coelomic fluid sex steroid hormone levels were measured in the sturgeon (Acipenseridae) at the onset of anadromous migration and maturation. Cortisol and testosterone levels in coelomic fluid were lower than in serum; conversely, progesterone levels were higher in coelomic fluid than in blood. Specific androgen and estrogen binding in the cytosol of different parts of the brain and in the gonads of fish were different in the pre-spawning state and after ovulation. Before spawning, the highest levels of specific androgen binding were in the forebrain, where levels decreased significantly after ovulation. Specific estrogen binding in the hypothalamus was significantly higher after maturation and ovulation. Correlations were established between sex steroid concentrations in the blood and levels of specific binding in the brain and gonads.