The effect of ambient oxygen concentration on filtering and respiration rates of <i>Daphnia galeata mendotae</i> and <i>Daphnia magna</i>1

Abstract

The filtering and respiration rates of Daphnia magna and Daphnia galeata mendotae were measured in oxygen concentrations ranging from air saturation to near zero, using animals that had lived in air‐saturated conditions so that facultative hemoglobin synthesis was not initiated. Daphnia magna ’s filtering and respiration rates are independent of oxygen concentrations above 3.0 mg liter −1 ; below this, rates decline rapidly. Daphania galeata mendotae ’s filtering and respiration rates exhibit’ a linear dependence on oxygen concentrations. It is suggested that D. magna ’s relatively greater tolerance of low oxygen concentrations is due largely to its higher basal levels of hemoglobin. Daphnia may often be oxygen limited in nature.