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

Abstract

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.