SCALING OF ANAEROBIC METABOLISM DURING EXERCISE IN THE ESTUARINE CROCODILE (CROCODYLUS-POROSUS)

The allometry of anaerobic metabolism was examined in wild estuarine c rocodiles (Crocodylus porosus) exercised to exhaustion during capture, with the aim of identifying factors underlying the higher anaerobic c apacity but possibly lower anaerobic scope in larger animals, Exercise time to exhaustion, and concentrations of lactate and protons in bloo d and tail muscle, increased with increasing body mass, Muscle glycoge n, both before and after exercise, also showed positive allometric sea ling, Muscle intracellular pH buffering capacity scaled negatively wit h body mass, The effects of pH on the activities of muscle phosphoryla se and phosphofructokinase were independent of body mass, It is propos ed that anaerobic capacity may be limited by the size of muscle glycog en reserves in smaller crocodiles and by glycolytic inhibition at the lower pH values encountered in larger crocodiles, Mean anaerobic scope , and phosphorylase activity in tail muscle, decreased with increasing body mass, while lactate dehydrogenase activity was independent of bo dy mass, Negative allometric scaling of anaerobic scope in crocodiles may relate to changes in predator-prey and social interactions that in volve reduced dependence on frequent bursts of anaerobic muscle work w ith increasing body mass.