Sex steroids in intersexual fishes

Studies of thein vitro gonadal steroidogenesis in intersexual fishes, using labelled testosterone as precursor, showed large species variation. The protogynousMonopterus albus produced predominantly 5α-reduced metabolites while the protandrousRhabdosargus sarba produced mainly 5β-reduced products. Both fishes synthesized 11-oxotestosterone; the synthesis of which appeared to mediate mainly through adrenosterone inM. albus butvia 11β-hydroxytestosterone inR. sarba.When the plasma levels of androstenedione, testosterone, 11-oxotestosterone, 11β-hydroxytestosterone, estrone and 17β-estradiol among the male, intersexual and female phase of the same species were compared, available data showed that either there was no obvious difference among the different sexual phases or the differences could be accounted for by the seasonal reproductive activities of the animal.Except for androstenedione, there are no marked changes in plasma testosterone, 11-oxotestosterone, 11β-hydroxytestosterone, estrone and 17β-estradiol levels in the intersexual phase compared with the female and male, it is unlikely that these classical sex steroids act as a primary trigger of natural sex reversal in these fishes; the role of androstenedione awaits further elucidation.