RESPIRATION OF FISHES WITH SPECIAL EMPHASIS ON STANDARD OXYGEN CONSUMPTION: III. INFLUENCE OF OXYGEN

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Abstract
Standard oxygen consumption was determined in relation to various partial pressures of oxygen for eastern brook trout at 10° and 15 °C, and for carp and goldfish at 10° and 20 °C. Two conditions of oxygen acclimation were compared. In one case acclimation was to air saturation while in the other acclimation was to each of the partial pressures of oxygen applied.Down to a partial pressure of oxygen of approximately 80 mm Hg, standard oxygen uptake remained approximately constant, and further, the rates for the two differently acclimated groups were about equal. Below 80 mm Hg the standard rate first increased to a maximum and then, with a further reduction in the partial pressure, decreased. Below 80 mm Hg the standard rate of oxygen consumption was in all cases less for the fish acclimated to the low level of oxygen than for those acclimated to air saturation.Comparison of standard and active values suggests that the increase in standard rate of oxygen uptake in response to low oxygen does not reach the active level as suggested earlier by Fry (1947). The suggestion is made that a fraction of standard metabolism is derived anaerobically in low levels of oxygen. Further, it appears that acclimation to a low level of oxygen enhances the anaerobic fraction of standard metabolism.