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Field and laboratory approaches to understanding testicular oocytes and gonadal development in smallmouth bass in relation to exposure to EACs
Citation:
Kadlec, S., R. Johnson, Dave Mount, AND P. Schoff. Field and laboratory approaches to understanding testicular oocytes and gonadal development in smallmouth bass in relation to exposure to EACs. SETAC North America, Orlando, FL, November 06 - 10, 2016.
Impact/Purpose:
Not applicable
Description:
In previous work we reported smallmouth bass populations in Northeastern Minnesota rivers and lakes with testicular oocyte (TOs) prevalence ranging from 7 to 59%, which is consistent with reports from other U.S. river systems. While it is often presumed that TOs are associated with exposure to endocrine active compounds (EACs), our analysis suggested only a weak relationship. To better understand gonadal development in smallmouth bass and how it might be influenced by exogenous estrogens, we conducted two laboratory exposures using 17-?-ethinyl estradiol (EE2). In experiment 1, smallmouth bass fry were exposed to 2 or 10 ng/L EE2 for 90 d beginning at swim-up, then reared for an additional 90 days in clean water. Treatment and control groups weresubsampled intermittently for histological evaluation of gonadal development. In fish exposed to 2 ng/L EE2, 100% developed ovaries by day 63. The ovaries continued to develop even after cessation of EE2 exposure. In experiment 2, smallmouth bass fry were exposed to 0.11, 0.33, 1.0, or 3.0 ng/L EE2 for 100 days, and evaluated for gonadal development at days 90 and 120. In the group exposed to 3 ng/L EE2, 100% of fish developed ovaries, while all groups exposed to lower concentrations showed a roughly 50:50 female-to-presumed male sex ratio. No TOs were observed in any fish exposed to concentrations of EE2 lower than that which caused presumptive sex reversal. This result suggests that wild smallmouth bass TOs may not be caused by juvenileexposure to estrogenic compounds.