Certain chemicals including industrial intermediates, PAHs, PCBs, pesticides, dioxins, trace elements and plant sterols has the capability to interfere with the endocrine system in fish. The potency of most of these chemicals, however, is typically hundreds to thousands of times less than that of endogenous hormones. Evidence of environmental endocrine disruption in fishes ranges from the presence of female egg proteins in males and reduced levels of endogenous hormones in both males and females, to gonadal histopathologies and intersex (presence of ovotestes) fish.
Keywords: Estrogen Receptor, Vitellogenin, EDCs, Ovotestis
The presence and effects of EDCs is not a new phenomenon. As early as 1949, it was known that crop dusters handling dichlorodiphenyltrichloroethane (DDT) frequently had reduced sperm counts (Patlak, 1996). DDT was shown to produce characteristically estrogenic responses in the reproductive tracts of rats and birds (Bitman and Cecil, 1970). The tragic use of the synthetic estrogen diethylstilbestrol, or DES, by pregnant women from the late 1940s until 1971 to help prevent miscarriages resulted in infertility and increased rates of vaginal clear cell adenocarcinomas in daughters (Colborn et al., 1993).
Fish as models for evaluating EDC.
EDCs are commonly present in the aquatic environments in combination with each other together with many other differently acting substances. Fish are a group of animals most at threat from aquatic pollution and with their physiological similarity to mammals including humans (Kime, 1998). Many of the investigations into EDCs in the aquatic environment have involved fish because of similarities in the endocrine system to higher vertebrates (Bond, 1979) . Fish are vertebrates and therefore have a close evolutionary relationship to mammals. Thus, mechanisms discovered in fish are more likely to be relevant to humans.
Structural similarities of EDCs with endogenous hormones
The most outstanding characteristics of EDCs is the structural resemblance it has with body’s endogenous estrogenic and androgenic hormones, an ability to interact with hormone transport proteins, or an ability to disrupt hormone metabolism, these chemicals have the potential to mimic, or in some cases block, the effects of the endogenous hormone. This structural similarity aids in the endocrine disruption phenomena. The structural relationship is presented by showing the chemical structures of some endogenous sex steroid hormones and some potent EDCs.