Nitroaromatic compounds frequently contaminate aquatic systems and may, therefore, impact fish. However, a known pathway of nitroaromatic toxicity in mammals, that of nitroaromatic stimulated superoxide (O2-) production, has yet to be addressed in fish. In this study we investigated this pathway in three species of freshwater fish-channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salmoides) and rainbow trout (Salmo gairdneri)-exposed to nitrofurantoin (NF), p-nitrobenzoic acid (PNBA) and m-dinitrobenzene (MDNB). Our results indicate that these nitroaromatics elicit a stimulation of O2- production by fish liver fractions. Additionally, results suggests a similarity between, fish and mammals in the nitroreductases which mediate nitroaromatic activation and subsequent O2- production. These findings indicate a potential toxic consequence of fish exposure to nitroaromatic contaminants in aquatic systems. © 1988.