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

Lactate concentration ([lactate−]), pH, and bicarbonate concentration ([HCO3−]) were measured in the blood of salt-water crocodiles (Crocodylus porosus Schneider) exhausted during field capture. Body temperature after capture averaged 31·1 °C. 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. Peak levels of [lactate−] increased with increasing body mass (slope = 9·72 mmol 1−1 logM−1; mass M in kg), indicating a greater anaerobic capacity in larger animals. Several large crocodiles had [lactate−] in excess of 50mmol 1−1. Blood pH decreased with mass (slope = 0·163 pH unitslogM−1) and reached 6·6 in the largest animals. One animal remained acidotic for several hours and had a minimal pH of 6·42. Blood increased significantly and [HCO3−] decreased significantly with increasing body mass. 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. During recovery, mean blood [lactate−] decrement after 2h was 6·0 mmol 1−1 and was not significantly related to mass. Proton elimination from the blood, however, was more rapid in larger animals (slope = 0·0443 μmol 1 −1 log M −1 ). The positive mass-dependence of acid-base disturbance could be related to the greater susceptibility of large crocodiles (>700 kg) to post-capture mortality.