Nitrogenous pollutants are commonly found in freshwater ecosystems due to fertilizer and chemical runoff from farm land and industrial waste. Nitrogenous compounds can result in toxic effects on aquatic vertebrates and invertebrates. The aim of this study was to determine the effects of ammonium nitrate, urea, and sodium nitrate on mosquitofish (Gambusia affinis) survivorship. Ammonium nitrate had a significant negative effect on survivorship, but urea and sodium nitrate had no effect on survivorship. This suggests that mosquitofish may be susceptible to ammonia pollution, but probably can tolerate most environmentally relevant exposures to urea and nitrate.