There is widespread concern that some environmental chemicals can reduce th
e reproductive capability of humans and wildlife by mimicking natural estro
gens and disrupting endocrine function. This potential threat to animal pop
ulations posed by xenoestrogens has, hardly surprisingly, been met by an in
tensive global effort to identify and develop biomarkers suitable for scree
ning chemicals for estrogen mimicking capacity. Despite this effort, there
are few biomarkers capable of linking exposure to xenoestrogens to impaired
reproductive capability. The reproductive success of most animals depends
strongly on the ability to perform the appropriate sexual behavior. The sex
ual display of the male guppy is strongly linked to reproductive success an
d is readily quantified under laboratory conditions. This preliminary study
demonstrates that exposure of adult male guppies to water weakly contamina
ted with either natural estrogen (17 beta-estradiol) or the xenoestrogen (4
-tert-octylphenol) causes a dramatic decrease in the rate and intensity of
sexual display, It is concluded that quantitative analysis of the sexual di
splay of male guppies holds great promise as a biomarker at the organismal
level for the effects of estrogen mimicking xenobiotics. (C) 1999 Academic
Press.