Oxygen uptake and carbon dioxide excretion by the branchial and postbranchial regions of adults of the lampreyGeotria australis in air

Abstract

O2 uptake and CO2 excretion by the branchial and postbranchial regions of adults of the lamprey Geotria australis have been measured in humidified air at 15 and 5°C. At 15°C, the mean standard V˙O2for whole animals was 31.9 μl·gm–1·hr–1, which is similar to the interpolated V˙O2in water at the same temperature and time of year. The corresponding mean standard V˙CO2was 25.2 μl·gm–1·hr–1, producing an RQ of 0.79. The branchial region was responsible for ˜87% of O2 uptake and ˜80% of CO2 excretion, which indicates that the gills of lampreys retain their integrity in air and thereby facilitate gas exchange. The continuous pumping of the branchial chamber would also facilitate gas exchange across the gills. The RQ is far higher in the postbranchial than branchial region, i.e., 1.26 vs. 0.72. The proportionately greater excretion of CO2 than uptake of O2 by the postbranchial than branchial region is presumably related to a combination of the greater capacitance of tissue for CO2 than O2 and the presence of a thicker tissue barrier in the skin of the trunk and tail than in the lamellae of the gills. At 5°C, the mean standardV˙O2andV˙CO2for whole animals declined markedly to 13.1 and 13.5 μl·gm–1·hr–1, respectively. The corresponding rise in RQ from 0.79 at 15°C to 1.03 at 5°C implies that aerobic metabolism now utilizes solely carbohydrate, rather than lipid and some carbohydrate. The transfer to solely carbohydrate metabolism at 5°C may be triggered by a need to supplement aerobic metabolism with anaerobic metabolism to compensate for an apparent shortfall in oxygen uptake produced by inadequate ventilation of the gills. J. Exp. Zool. 278:290–298, 1997. © 1997 Wiley-Liss, Inc.