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Journal of Experimental Biology 118,161-171 (1985)
Published by Company of Biologists 1985

Mass-Dependence of Anaerobic Metabolism and Acid-Base Disturbance During Activity in the Salt-Water Crocodile, Crocodylus Porosus

A. F. BENNETT ¹, R. S. SEYMOUR ², D. F. BRADFORD ², and G.J. W. WEBB ³

¹ School of Biological Sciences, University of California, Irvine, California 92717 U.S.A.
² Department of Zoology, University of Adelaide, Adelaide, S.A. 5001
³ Conservation Commission of the Northern Territory, P.O. Box 38496, Winnellie, N.T. 5789, Australia

1. Lactate concentration ([lactate^-]), pH, Pco₂, Po₂ and bicarbonate concentration ([HCO3^-]) were measured in the blood of salt-water crocodiles (Crocodylus porosus Schneider) exhausted during field capture.

2. Body temperature after capture averaged 31.1°C.

3. All animals underwent high levels of anaerobic metabolism and metabolic acidosis. The largest animals attained the highest blood [lactate^-] and lowest pH ever observed in any animal as a result of activity.

4. Peak levels of [lactate^-] increased with increasing body mass (slope=9.72 mmoll^-1 logM^-1; mass M in kg), indicating a greater anaerobic capacity in larger animals. Several large crocodiles had [lactate^-] in excess of SOmmoll^-1.

5. Blood pH decreased with mass (slope=0.163 pH units log M^-1) and reached 6.6 in the largest animals. One animal remained acidotic for several hours and had a minimal pH of 6.42.

6. Blood Pco₂ increased significantly and [HCO₃^-] decreased significantly with increasing body mass.

7. Struggling time before exhaustion was greater in larger animals, ranging from about 5min in small (<1 kg) crocodiles to over 30min in animals over 100 kg.

8. During recovery, mean blood [lactate^-] decrement after 2h was 6.0mmoll^-1 and was not significantly related to mass. Proton elimination from the blood, however, was more rapid in larger animals (slope=0.0443 µmoll^-1 log M^-1).

9. The positive mass-dependence of acid-base disturbance could be related to the greater susceptibility of large crocodiles (>700kg) to postcapture mortality.

Key words: Anaerobic capacity, pH, mass-dependence, reptile

Accepted on March 20, 1985