Their unique hydrological and climatic conditions render surface water systems in the southern Canadian Prairies at an elevated risk from exposure to contaminants released from municipal wastewater effluents (MWWEs). The aim of this study was to characterize the potential health effects and their underlying molecular mechanisms in populations of fathead minnow (Pimephales promelas; FHM) in Wascana Creek, an effluent dominated stream in Southern Saskatchewan, Canada. Studies were conducted during the spawning season in 2014 and 2015 to assess responses in terms of overall health, reproductive functions, plasma sex steroid hormone levels, and expression of selected genes along the hypothalamus-pituitary-gonadal axis. FHM downstream of the effluent fallout had lower gonadosomatic indices and significantly greater hepatosomatic indices compared to upstream populations. In both male and female FHMs, significantly greater occurrence and severity of gonadal degradation and delayed maturation were observed in downstream fish compared to upstream fish. Downstream males also displayed lower scores of secondary sexual characteristics and a decreasing trend in plasma 11-ketotestosterone levels. Interestingly, no indications of exposure to estrogenic compounds, such as occurrence of testicular oocytes were observed, which was in accordance with the lack of presence of key biomarkers of estrogenic exposure, such as induction of vitellogenin. In general, expression of the majority of transcripts measured in FHMs downstream of the effluent fallout was significantly downregulated, which supports observations of the general deterioration of the health and reproductive status of these fish. Chemical analysis indicated that 10 pharmaceuticals and personal care products (PPCPs) were present at the downstream site, some at sufficiently great concentrations that may present a risk to aquatic organisms. With continuous exposure to a diverse number of stressors including high nutrient and ammonia levels, the presence of a variety of PPCPs and other contaminants, Wascana Creek should be considered as an ecosystem at risk.

独特的水文和气候条件使得加拿大南部大草原的地表水系统面临着较高的暴露于城市废水排放物（MWWE）污染物的风险。本研究的目的是表征瓦斯卡纳溪（加拿大萨斯喀彻温省南部的一条污水主要河流）黑头鲦鱼（ Pimephales promelas ；FHM）种群的潜在健康影响及其潜在分子机制。在 2014 年和 2015 年产卵季节进行了研究，以评估整体健康、生殖功能、血浆性类固醇激素水平以及下丘脑-垂体-性腺轴上选定基因的表达方面的反应。与上游群体相比，污水沉降物下游的 FHM 具有较低的性腺体指数和显着较高的肝体指数。在雄性和雌性 FHM 中，与上游鱼类相比，下游鱼类的性腺退化和延迟成熟的发生率和严重程度明显更高。下游男性的第二性征得分也较低，血浆 11-酮睾酮水平呈下降趋势。有趣的是，没有观察到暴露于雌激素化合物的迹象，例如睾丸卵母细胞的出现，这与缺乏雌激素暴露的关键生物标志物（例如卵黄蛋白原的诱导）一致。一般来说，在污水沉降物下游的 FHM 中测量的大多数转录本的表达显着下调，这支持了对这些鱼的健康和繁殖状态普遍恶化的观察。 化学分析表明，下游地点存在 10 种药品和个人护理产品 (PPCP)，其中一些浓度足够高，可能对水生生物构成风险。由于持续暴露于多种压力源，包括高营养物和氨水平、各种 PPCP 和其他污染物的存在，瓦斯卡纳溪应被视为处于危险之中的生态系统。