Feminized Male Fish in Santa Monica Bay

Feminized Male Fish in Santa Monica Bay



  • Hornyhead turbot males show high levels of the female sex
    steroid hormone estradiol
  • Two potential reasons why this could be occuring:

1) Fish being exposed to human hormones through environment
2) Fish gonads are accidentally making the female hormone


Santa Monica Bay

With collaborators at several municipal sanitation districts, California State
University-Long Beach, University of California-Riverside and other
agencies, we are participating in a study that has found that males of a
particular fish species, the hornyhead turbot Pleuronichthys verticalis, are
exhibiting very high levels of the female sex steroid hormone, estradiol.
Males tested from Santa Monica Bay appear to have some of the highest
estradiol levels of any fish sampled in southern California.  These males
show estradiol levels as high as reproductive female fish.  Our ongoing work
is trying to find out why this is happening.  One possibility is that the fish are
accumulating the steroid hormone from their environment, which receives
waste water from two of the largest treatment plants in the world.  Human
urine contains significant amounts of estradiol, and when millions of humans
must urinate, this means a large amount of the hormone may leak into the
environment.  This possibility is being closely studied.  Another possibility is
that the males gonads may be “accidentally” making the estradiol, which
could possibly result from the conversion of testosterone by certain enzymes
that should not be expressed in males.  There is some precedent in the
scientific literature that certain chemicals may turn “on” this enzyme
pathway –if so, it would be a type of chemically induced “endocrine
disruption”.  This possibility is also being closely studied.  These scientific
findings are unique to wildlife residing in a marine environment, and they
may help us to identify important reproductive effects from human-derived



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