Mechanism for maintaining oxygen consumption under varying oxygenation levels in the freshwater clam Corbicula fluminea

The basic adaptation mechanisms that allow the Asian freshwater clam Corbic ula fluminea to maintain its oxygen (O-2) consumption constant under restin g conditions when the partial pressure of O-2 (P-O2) in the water varies fr om 4 to 40 kPa were studied at plankton concentrations which were high enou gh that ventilation was not affected. Steady-state values for O-2 consumpti on, P-O2, and O-2 concentration in the arterial and venous blood, P-O2 in t he expired water, and ventilatory and circulatory blood flow were determine d after 24-h periods of exposure to selected water P-O2 values. The key ada ptation after 1 day of acclimation was the maintenance of O-2 consumption, which was achieved exclusively by ventilatory adjustment, with no change in the oxygenation status of the internal milieu. Specifically, arterial P-O2 remained constant at 3 kPa and venous P-O2 at 2 kPa. Arterial and venous b lood O-2 concentrations and blood-flow rate also remained constant. The dat a are discussed in terms of feeding versus respiratory control of ventilati on in filter-feeders in an environmental context. The agreement between the homeostasis strategy described here and previous results reported for the freshwater mussel Anodonta cygnea, crustaceans, and teleosts is emphasised.