Models and Murkiness: Evaluating Fish Endocrine Disruption In the Laboratory and the Field
Coastal Sciences, Gulf Coast Research Laboratory
Ocean Science and Engineering
Much analysis of endocrine disruption in fishes has focused on measuring vitellogenin as a biomarker of estrogenic disruption. Vitellogenin (VTG) is a specific and convenient marker of estrogen exposure, but it does not provide information about effects on sexual development, reproductive success, or other subtle changes in reproductive physiology. Using medaka as a model system, we conducted two laboratory studies evaluating multiple endpoints of endocrine disruption. In the first, we examined the effects of anthracene as a potential estrogen antagonist and in the second, we examined the effects of DDT as an estrogen agonist. For both compounds, developing medaka were exposed for either two or eight weeks post-hatch. Subsamples were taken after 2, 4, and 8 weeks for quantification of vitellogenin (both compounds) and histological examination of the gonads (DDT exposed fish). After fish reached sexual maturity, mating pairs established. Percentage of fertilized eggs and percentage of embryos surviving 16 days post-hatch were quantified. Two week exposure to anthracene had no effect on mating success, but reduced the proportion of estrogen-induced sex reversal in co-exposed fish. Eight week exposure to anthracene reduced the percentage of fertilized eggs and co-exposure to estradiol prevented the anthracene effect. We concluded that anthracene disrupts estrogen action, but not via the estrogen receptor as no changes in VTG production occurred. In the second laboratory study, we found that DDT feminized developing fish, producing a female-skewed sex ratio in adults after both 2 and 8 week exposures. Fertility and hatching success were significantly reduced in a time and dose dependent manner. DDT had no effect on VTG expression after a 2 week exposure, but did induce VTG production after 8 weeks. However, fertility and hatching success were more sensitive to estrogenic disruption than were gonad differentiation and VTG expression. These laboratory studies clearly showed multiple effects of endocrine disruption by xenobiotics. Field studies tend to be murkier. How prevalent is endocrine disruption in wild fish and what is its impact? Our field work has focused on Iongear sunfish (Lepomis megalotis) exposed to unbleached kraft mill effluent. Fish were sampled twice monthly during the spring and summer reproductive season and once monthly during the fall and winter of the past two years. Males and females were captured and bled for analysis ofVTG, estradiol, testosterone (T), and 11-ketotestosterone (l lKT) levels. Males upstream and downstream of the effluent outfall have similarly low levels ofVTG, indicating that they are not exposed to an estrogenic substance. Males downstream of the outfall have slightly lower T levels and slightly higher estradiol levels than males upstream and the ratio of T to estradiol is significantly lower in downstream males, indicating that exposure to mill effluent has a slightly demasculinizing effect on males. VTG and hormone levels do not differ in females upstream and downstream of the effluent. We conclude that there is a subtle effect of kraft mill effluent on reproductive physiology of adult male sunfish, but no morphological effects are evident. Endocrine disruption is occurring in wild populations, but we still can't fully measure the impacts.
Proceedings of the 3rd International Conference On Pharmaceuticals and Endocrine Disrupting Chemicals In Water
Cheek, A. O.,
Fentress, J. A.,
Steele, S. L.,
Bart, H. L.,
(2003). Models and Murkiness: Evaluating Fish Endocrine Disruption In the Laboratory and the Field. Proceedings of the 3rd International Conference On Pharmaceuticals and Endocrine Disrupting Chemicals In Water.
Available at: https://aquila.usm.edu/fac_pubs/17270