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Laboratory approaches to understanding gonadal development and abnormalities in wild-caught smallmouth bass (Micropterus dolomieu)
Citation:
Kadlec, S., R. Johnson, Dave Mount, AND P. Schoff. Laboratory approaches to understanding gonadal development and abnormalities in wild-caught smallmouth bass (Micropterus dolomieu). SETAC North America, Salt Lake City, UT, November 01 - 05, 2015.
Impact/Purpose:
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Description:
Our previous work reported smallmouth bass in Northeastern Minnesota rivers and lakes with a prevalence of testicular oocytes (TOs) ranging from 7 to 57%, which is consistent with findings reported in other U.S. river systems. While it is often presumed that TOs are caused by exposure to estrogenic compounds, the relatively high prevalence of TOs in some waters with no known source of estrogenic compounds suggests an alternate or more complex explanation. To better understand gonadal development of smallmouth bass and how it is influenced by estrogenic exposure, we conducted a laboratory exposure using 17-á-ethinyl estradiol (EE2). Smallmouth bass fry were exposed for 90 d to 2 or 10 ng/L EE2 beginning at swim-up, then reared for an additional 90 days in clean water. These treatment groups and control fish were subsampled intermittently for histological evaluation of gonadal development. In control fish, subtle indications of ovarian differentiation were observed at 32 d, with unambiguous distinction of ovaries from undifferentiated (presumed male) gonads by day 63, and formation of clearly identifiable testicular tissue by day 92. In the groups exposed to 2 ng/L EE2, 100% of fish had undergone ovarian differentiation by day 63, with continued development of ovaries even after cessation of EE2 exposure. Because no EE2-exposed fish followed a path of testicular development, the connection between testicular oocytes and estrogenic exposure could not be evaluated. Given that total estrogenicity at or near the equivalent of 2 ng/L EE2 has been measured in or near wastewater treatment plant discharges, our study suggests that smallmouth bass could be susceptible to estrogenic exposure in the environment. Ongoing studies are focused on determining response to lower intensity exposures.