Gas exchange in the cephalopod, Octopus dofleini

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Abstract
Gas exchange has been studied in free swimming specimens of the large Cephalopod, Octopus dofleini. Arterial and venous blood samples were analyzed for respiratory gases and pH. Ventilation and partial pressures of O2 in inspired and expired water were also measured. Marked difference in O2 tension was found between the efferent water (PeO2) and the arterial blood (PaO2). The difference is discussed in relation to the presence of an anatomical and physiological dead space or shunting of blood through nonrespiratory parts of the gills. PaO2 showed rather low values ranging from 58 to 108 mm Hg, with an average of 77.5 mm Hg. Such values are below the partial pressures needed to secure complete saturation of the blood. PO2 in venous blood averaged 9.7 mm Hg. It is suggested that a potential O2 reserve in the blood lies in a more complete saturation of the arterial blood. The octopus showed high values for ventilation and extremely low values of PCO2, in blood. These results are used to point out basic differences between aquatic and aerial gas exchange. Extraction of O2 from the water averaged 27% over the range of PIO2 observed in these experiments. It was also found to rise with a fall in PIO2. The physiological importance of the Bohr and Haldane effects is evaluated. The respiratory quotient was calculated from the arteriovenous difference in O2 and CO2 content. The significance of the unusually high values obtained for RQ is discussed.

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