Fish Intersexuality as Indicator of Environmental Stress summarizes a presentation about using intersexuality in fish as a bioindicator for detecting endocrine disrupting chemicals in bodies of water. The presentation describes research on mosquitofish and least killifish exposed to kraft-mill effluent that showed masculinized features in female fish, including gonopodial elongation of the anal fin in mosquitofish and increased segmentation at the fin ray tips in least killifish. The study demonstrates that examining reproductive systems in fish can help identify substances interfering with hormone-mediated processes and that poeciliid fish make useful subjects for detecting endocrine disruptors.