ABSTRACT
Oxygen uptake in the crayfish Orconectes rusticus was maintained at nor-moxic levels throughout 6 days exposure to an ambient oxygen tension of 45–55 torr. This was attributed to compensatory responses of the ventilatory and cardiovascular pumps. The first 72 h of hypoxic exposure were characterized by a transitory 3-fold increase in both scaphognathite rate and cardiac output above initial normoxic values. During the latter 72 h of hypoxic exposure both scaphognathite pumping and cardiac output were significantly below maximum values but were maintained above initial normoxic levels. Thus, as reflected by the increased convection requirements for both water and haemolymph, the increased scaphognathite and heart activity served to increase oxygen delivery to both the branchial chambers and the tissues. Additionally, the increased branchial ventilation and gill perfusion facilitated removal of dissolved carbon dioxide from the haemolymph, effecting a respiratory alkalosis. The increased haemolymph pH elevated the oxygen affinity of the haemocyanin via the Bohr affect, enabling a greater volume of oxygen to be picked up at the gills by the haemocyanin despite the reduced pressure gradient.
