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

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.

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 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.

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.

Blood Pco₂ 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 6.0mmoll⁻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).

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