Artificial-induced sex reversal and paradoxical sex reversal in medaka

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Using six medaka inbred strains, their sex reversal process after administration of sex steroids to embryos were investigated. After estrogen administration, XY females were appeared in 5 strains, but the sensitivity and/or degree of sex-reversal were different among strains. Administration of androgen to XX specimen caused female to male sex reversal in various degree. On the other hand, male to female sex reversal in XY specimens termed paradoxical sex reversal were also observed at high dose of androgen in 4 strains. Thus the sex reversal process were highly varied among strains. In most strains, gonads showed strong atrophy after androgen administration. After hatching when clearing the exogenous androgen, these gonads were eventually recovered but their growth and the sexual differentiation were remarkably delayed.