Reproductivity and gonad histology in sex transformed medaka Oryzias latipes exposed to 17β-estradiol with different exposure period

Abstract

Sex transformed medaka exposed to 17β-estradiol (E2) in short-term exposure (egg-larva period) and long-term exposure (egg-adult period) was examined the reproductive character in fecundity, spawning times, and fertility. Most genetic males were transformed to phenotypic female by E2 in both exposure periods. On the other hand, reproductivity and GSI of sex-transformed female (XY female) in long-term exposure are lower than that of XY female in short-term exposure and of normal female (XX) in control. In gonad histology of XY females, those in short-term exposure possessed well-matured ovary as well as XX female in control. On the other hand, most XY females in long-term exposure possessed immature ovary, especially, most oocytes are in pre-vitellogenic phase. From these results, it is considered that the exposure to E2 until the end of larval period induce the sex-transformed medaka with high reproductivity as well as XX female in control, but suggesting that the longer exposure to E2 might inhibit to sexual maturation in XY female.