Altered sexual characteristics in guppies (Poecilia reticulata) exposed to 17beta-estradiol and 4-tert-octylphenol during sexual development.

The effects of estrogenic compounds on the development of sexual characteristics in juvenile guppies (Poecilia reticulata) were examined. After exposure for 3 months, the sex ratio was female biased in guppies exposed to 0.5 microg/L 17beta-estradiol (E2) or higher but unaffected by exposure to 4-tert-octylphenol (OP). When exposed to 100 microg/L OP, the male guppy sexual behavior and sperm count were increased. In contrast, the male sperm count was markedly reduced after exposure to a high concentration of E2. The length of the gonopodium (copulatory organ) was increased when exposed to 100 microg/L OP and at all the tested concentrations of E2. Similar concentrations of OP and E2 reduced the gonad weight of the females. The results demonstrate that the development of sexual characteristics in guppies can be disturbed by environmentally realistic concentrations of E2 but higher concentrations of OP are needed to induce similar alterations.