Plasma profiles of fourteen ovarian steroids before, during and after ovulation in African catfish,Clarias gariepinus, determined by gas chromatography and mass spectrometry.

The plasma concentrations of fourteen ovarian steroids were measured in postvitellogenic African catfish,Clarias gariepinus, which had been injected with pimozide and LHRHa. Postvitellogenesis persisted for at least four hours after pimozide and LHRHa administration. During this stage a limited rise in the plasma gonadotropin (GTH) level was accompanied by an increase in the testosterone concentration. The estradiol level was high and remained high except for a passing drop during the stage of germinal vesicle migration. At the stage of germinal vesicle migration a strong increase in the plasma GTH level coincided with a maximum in the testosterone concentration and a concomitant increase in the levels of 17α,20β-dihydroxy-4-pregnen-3-one and of five 5β-reduced pregnanes. During germinal vesicle breakdown the GTH concentration remained high, the plasma level of 17α-hydroxyprogesterone tended to increase, and the levels of 5β-pregnane-3α, 17α-diol-20-one, 5β-pregnane-3α,17α,20β-triol and 5β-pregnane-3α,17α,20α-triol reached a maximum. At pre-ovulation the GTH concentration did not change, and peak levels were reached of 17α,20β-dihydroxy-4-pregnen-3-one and 5β-pregnane-3α,6α,17α-triol-20-one. Shortly after ovulation the GTH concentration slightly decreased together with a sharp decline in the concentrations of 17α,20β-dihydroxy-4-pregnen-3-one and the 5β-reduced steroids, with the exception of 5β-pregnane-3α,17α,20α-triol, 5β-pregnane-3α,6α,17α,20β-tetrol and 5β-dihydrotestosterone. The plasma concentrations of androstenedione, estrone, etiocholanolone and 5β-androstane-3α,17β-diol showed marginal fluctuations during oocyte maturation and ovulation. Apart from 17α,20β-dihydroxy-4-pregnen-3-one, the 5β-reduced pregnanes might be candidates for the function of oocyte maturation inducing hormone inC. gariepinus.