OXYGEN-UPTAKE AND CARBON-DIOXIDE EXCRETION BY THE BRANCHIAL AND POSTBRANCHIAL REGIONS OF ADULTS OF THE LAMPREY GEOTRIA-AUSTRALIS IN AIR

O-2 uptake and CO2 excretion by the branchial and postbranchial region s of adults of the lamprey Geotria australis have been measured in hum idified air at 15 and 5 degrees C. At 15 degrees C, the mean standard (V) over dot (O2) for whole animals was 31.9 mu l.gm(-1).hr(-1), which is similar to the interpolated (V) over dot (O2) in water at the same temperature and time of year. The corresponding mean standard (V) ove r dot (CO2) was 25.2 mu l.gm(-1).hr(-1), producing an RQ of 0.79. The branchial region was responsible for similar to 87% of O-2 uptake and similar to 80% of CO2 excretion, which indicates that the gills of lam preys retain their integrity in air and thereby facilitate gas exchang e. The continuous pumping of the branchial chamber would also facilita te gas exchange across the gills. The RQ is far higher in the postbran chial than branchial region, i.e., 1.26 vs. 0.72. The proportionately greater excretion of CO2 than uptake of O-2 by the postbranchial than branchial region is presumably related to a combination of the greater capacitance of tissue for CO2 than O-2 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 degrees C, the mean standard (V) over dot (O2) and (V) over dot (CO2) for whole animals declined markedly to 13.1 and 13. 5 mu l.gm(-1).hr(-1), respectively. The corresponding rise in RQ from 0.79 to 15 degrees C to 1.03 at 5 degrees C implies that aerobic metab olism now utilizes solely carbohydrate, rather than lipid and some car bohydrate. The transfer to solely carbohydrate metabolism at 5 degrees C may be triggered by a need to supplement aerobic metabolism with an aerobic metabolism to compensate for an apparent shortfall in oxygen u ptake produced by inadequate ventilation of the gills. (C) 1997 Wiley- Liss, Inc.