Municipal wastewaters are a complex mixture containing estrogens and estrogen mimics that are known to affect the reproductive health of wild fishes. Male fishes downstream of some wastewater outfalls produce vitellogenin (VTG) (a protein normally synthesized by females during oocyte maturation) and early-stage eggs in their testes, and this feminization has been attributed to the presence of estrogenic substances such as natural estrogens [estrone or 17␤-estradiol (E2)], the synthetic estrogen used in birth-control pills [17␣-ethynylestradiol (EE2)], or weaker estrogen mimics such as nonylphenol in the water. Despite widespread evidence that male fishes are being feminized, it is not known whether these low-level, chronic exposures adversely impact the sustainability of wild populations. We conducted a 7-year, wholelake experiment at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada, and showed that chronic exposure of fathead minnow (Pimephales promelas) to low concentrations (5-6 ng⅐L ؊1 ) of the potent 17␣-ethynylestradiol led to feminization of males through the production of vitellogenin mRNA and protein, impacts on gonadal development as evidenced by intersex in males and altered oogenesis in females, and, ultimately, a near extinction of this species from the lake. Our observations demonstrate that the concentrations of estrogens and their mimics observed in freshwaters can impact the sustainability of wild fish populations.endocrine disrupters ͉ fathead minnow ͉ municipal wastewaters ͉ population-level effects ͉ whole-lake experiment

Elevated concentrations of Se have been detected in cold, flowing water habitats near uranium and coal mines in Canada. Fish from these systems have concentrations of Se in their tissues that exceed toxic effect thresholds that have been established for warm-water fishes. However, the applicability of toxic effect thresholds and guidelines to cold water, lotic habitats is a matter of contention in the literature since most cases of Se toxicosis have been documented in standing, warm-water systems. To examine the possibility of impaired reproduction in wild rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinusfontinalis) near coal mining activity in the northeastern slopes region of Alberta, Canada, spawn from both species were collected from exposure and reference sites. Gametes were fertilized in the laboratory, reared to the swim-up stage, and examined for deformities. A significant relationship was observed for rainbow trout between the amount of Se in eggs and the incidence of developmental abnormalities, specifically craniofacial defects, skeletal deformities, and edema. These associations approximate exponential functions with probabilities that 15% of the population would be affected occurring between 8.8 and 10.5 microg Se per gram of wet egg weight, based on probit analysis. These relationships are similar to those described for centrarchids inhabiting a seleniferous warm-water lake. No such relationships were established for brook trout.

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Potential effects of exposure to contaminants with estrogenic activity are currently being examined in fish from a lake experimentally treated with the synthetic estrogen, ethynylestradiol (EE2). EE2 was added to Lake 260, a small Precambrian shield lake in the Experimental Lakes Area (ELA) of northwestern Ontario, from late May to October 2001. Concentrations of EE2 in epilimnetic waters ranged between 4.0 and 8.1 ng/L, with a mean (±SD) of 6.0 ± 2.8 ng/L. Male fathead minnows (Pimephales promelas) captured from Lake 260 after EE2 additions began contained 9000-fold higher concentrations of the egg yolk precursor vitellogenin (VTG), than were detected in fish captured from the same lake prior to the EE2 additions, or when compared to fatheads from reference lakes during the same sample period. VTG in females was induced 8- to 80-fold and was sustained beyond the normal window of vitellogenesis in Lake 260. Histological examination of tissues from EE2-exposed male fatheads in Lake 260 showed widespread fibrosis and inhibition of testicular development. Enlargement of liver cells, edema in the interstitium between kidney tubules, and eosinophilic deposits in the kidney tubule lumen were also evident in male fatheads from Lake 260. Further studies will examine the relationships between biochemical and histological alterations and population level effects.

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