Blood Gases of the South American Lungfish, Lepidosiren paradoxa: A Comparison to Other Air-breathing Fish and to Amphibians

All blood gas samples were obtained during the nonaestivating period of the animals. The red cells of Lepidosiren are large and nucleated, which leads to a slow linear decline due to O₂ consumption of the cells. This O₂ consumption was corrected for by linear regression to zero time. As a less attractive alternative, the small animals might have been inadequate for implantation of catheters and subsequent blood sampling. Comparing Rana catesbeiana, to Lepidosiren it turns out that PaCO₂ of Lepidosiren is about twice the value for Rana catesbeiana. This result was not expected from the principle of Dejours, in particular because R. catesbeiana eliminates 59% of total CO₂ output by the lung, while the lungfish eliminates 50%. Cutaneous gas exchange is mainly diffusion dependent and Kco₂ increases by only 10%/10°C.