17α,20β-Dihydroxy-4-pregnen-3-one (17α,20β-DHP) is an endogenous, maturation-inducing steroid that stimulates oocyte maturation in females of several teleost species. For example, 1 μg/ml of 17α,20β-DHP applied to Persian sturgeon oocytes has been shown to effectively induce germinal vesicle breakdown, an essential step during oocyte maturation.1 Gonadotropin-releasing hormone and the gonadotropins, follicle-stimulating hormone and luteinizing hormone, have been shown to stimulate the production of 17α,20β-DHP either in vivo or in vitro.[2] 17α,20β-DHP has also been reported to influence spermiation by stimulating milt production when administered at 5 mg/kg to various male teleosts.[1]