Fertilizers increase yield of crops but may have unintended negative effects on fish as a byproduct of runoff into bodies of freshwater. The objective of this study was to determine if environmentally relevant concentrations of an ammonium fertilizer impacts stress and innate immunity in Western mosquitofish (Gambusia affinis). The mosquitofish were exposed to different concentrations of ammonium sulfate fertilizer: 0 ppm, 40 ppm, and 80 ppm. To test the effects of ammonium sulfate on stress physiology, cortisol released into water by individual fish was collected after 1 week of exposure and again after 2 weeks of exposure and quantified with an enzyme immunoassay. Cortisol levels in the 0-ppm group were not significantly different over the course of the study, but we found a significant increase in cortisol levels in the fish exposed to 40 ppm and 80 ppm. We found reduced survival in fish from the 40 ppm and 80 ppm of ammonium sulfate groups compared with the 0-ppm group. We also used blood samples to complete a lysozyme assay as a measure of innate immune defense. Higher concentrations of ammonium sulfate correlated with significantly lower lysozyme activity in the fish. Overall, our results suggest that relatively low amounts of ammonium sulfate runoff into bodies of water are likely to have negative sublethal and lethal effects on small fishes.

化肥可增加农作物的产量，但可能对鱼类产生意想不到的负面影响，这是流入淡水体内的副产品。这项研究的目的是确定环境相关浓度的铵肥是否会影响西部蚊鱼的应激和先天免疫力（Gambusia affinis）。蚊鱼暴露于不同浓度的硫酸铵肥料：0 ppm，40 ppm和80 ppm。为了测试硫酸铵对胁迫生理的影响，在暴露1周后和暴露2周后再次收集个别鱼类释放到水中的皮质醇，并通过酶免疫法进行定量。在研究过程中，0-ppm组的皮质醇水平无显着差异，但我们发现暴露于40 ppm和80 ppm的鱼的皮质醇水平显着增加。我们发现，与0 ppm组相比，硫酸铵40 ppm和80 ppm组的鱼类存活率降低。我们还使用血液样本完成了溶菌酶测定，以此来衡量先天免疫防御能力。较高浓度的硫酸铵与鱼中的溶菌酶活性明显降低有关。总的来说，我们的结果表明，进入水体的硫酸铵径流相对较少，可能会对小鱼造成亚致死和致死作用。