Serum vitellogenin levels and reproductive impairment of male Japanese medaka (Oryzias latipes) exposed to 4-tert-octylphenol

The induction of synthesis of the "female" yolk precursor protein vitellogenin (VTG) in male fish by estrogenic chemicals in the environment has been demonstrated in many recent reports. However, little is known about the organismal and biological significance of this phenomenon. To examine the relationship between VTG production in male fish and reproductive impairment, adult male medaka were exposed to 4-tert-octylphenol (OP), a known environmental estrogen, in concentrations ranging from 20 to 230 ppb for 21 days, under flow-through conditions. Following exposure, male fish were mated, in the absence of OP, with unexposed females. Breeding groups composed of exposed males and control females produced about 50% fewer eggs than control groups. VTG levels in serum of male fish increased with increasing OP exposure concentration and decreased after OP exposure was discontinued. Nevertheless, significant correlations (p<0.01) were observed between VTG levels in exposed male fish and 1) OP exposure concentrations, 2) percent of fertilized eggs, and 3) survival of embryos. OP-induced VTG synthesis and reproductive impairment appear to be closely linked phenomena. Histological examination indicated spermatogenesis in OP-exposed fish was inhibited, and some exposed fish had oocytes in their testes. Finally, OP caused a significant increase in the number of abnormally developing embryos, suggesting that OP may be genotoxic as well as estrogenic.