This study was designed to examine effects of low dissolved oxygen on finfish, lobster, and squid under field conditions in western Long Island Sound. The relationship between bottom dissolved oxygen (DO) and catch was examined for effects on abundance, numbers of species, and mean length, for trawl sites throughout the sound. Examination of mean catch per tow, and species number per tow, showed that both abundance and diversity decreased markedly with bottom DO, with dramatic declines at sites with DO<2 mg l−1. Of 18 species examined, 15 were found to occur with greater frequency at sites with DO>3 mg l−1 compared to sites with <2 mg l−1, and three of these species occurred significantly less frequency at a DO of 2–3 mg l−1. Trawl samples taken in the Narrows west of Greenwich, an area which chronically experiences summer hypoxia (DO<3 mg l−1) consistently yielded below average species number during hypoxic events. However, when DO was>3 mg l−1, 13 of 14 tows had above average species number. Abundance of five common species at sites>3 mg l−1 DO were significantly higher than at sites <3 mg l−1 DO in this area. Lobster was the only species not showing this DO threshold. Patterns in abundance vs DO for squid, bluefish, and butterfish suggest that these species are among the most sensitive to hypoxia. Only one of the four examined species, winter flounder, showed a decrease in mean length with DO. Scup, bluefish, and lobster lengths did not vary significantly with respect to dissolved oxygen.