The minimum oxygen requirements of the following five species of fish were studied under quiescent conditions. Lebistes reticulatus (Peters); Gambusia affinis (Baird and Girard); Pimephales promelas (Rafinesques); Hybognathus placitus (Girard); and Notropis girardi (Hubbs and Ortenburger). Nitrogen gas was bubbled through the waters in the test vessels to remove the dissolved oxygen. The fish were tested under varied temperatures and at different levels of oxygen depletion. All specimens tested were able to live at oxygen tensions of 1.0 ppm. The reactions of the fish varies with (1) the spread of oxygen removal, and (2) the species.