John Wiley & Sons, Ltd.

Occurrence and degree of intersex (testis‐ova) in darters (Etheostoma spp.) across an urban gradient in the Grand River, Ontario, Canada

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The variability and extent of the intersex condition (oocytes in testes or testis‐ova) in fish along an urban gradient, that included major wastewater treatment plant outfalls, was documented in the Grand River, Ontario, Canada. A rapid enumeration of testis‐ova method (RETO) was developed and applied that increased the capacity to quantify both intersex prevalence and severity. Male Rainbow Darters (Etheostoma caeruleum) sampled downstream of the first major wastewater outfall (Waterloo) had a significant increase, relative to four upstream reference sites, in the mean proportion of fish with at least one testis‐oocyte (t.o.) per lobe of testes (9–20% proportion with ≤ 1 t.o./lobe vs. 32–53% and >1.4 t.o./lobe). A much higher mean incidence of intersex proportion and degree was observed immediately downstream of the second wastewater outfall (Kitchener; 73–100% and 8–70 t.o./lobe) but only 6.3 km downstream of the Kitchener outfall the occurrence of intersex drops to those of the reference sites. In contrast, downstream of a tertiary treated wastewater outfall on a small tributary intersex was similar to reference sites. Estrogenicity, measured using a Yeast Estrogen Screen (YES), followed a similar pattern increasing from 0.81 ± 0.02 ng/L EEq (Guelph), to 4.32 ± 0.07 ng/L (Waterloo), and 16.99 ± 0.40 ng/L (Kitchener) respectively. Female Rainbow Darter downstream of the Kitchener outfall showed significant decreases in gonadosomatic index (GSI) and liver somatic index (LSI), and increases in condition factor (k) relative to corresponding reference sites. The prevalence of intersex and alterations in somatic indices suggest that exposure to municipal wastewater effluent discharges can impact endocrine function, energy use, and energy storage in wild fish. Environ Toxicol Chem © 2013 SETAC

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