Reactions of some great plains fishes to progressive hypoxia

Twenty-six species from eight families of great plains fishes were examined in progressive hypoxia to see if the use of dissolved O 2 in the surface film was common when subsurface waters became hypoxic. Only the Salmonidae (three species) and Stizostedion vitreum did not move to the surface and breathe the surface film. The concentration of dissolved O 2 at which this reaction occurred was found to be strongly temperature dependent in Pimephales promelas. During progressive hypoxia all fishes exhibited a similar sequence of behavioural events. Particular points in this sequence were used to estimate incipient limiting and lethal levels of dissolved O 2 .