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

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.