Diving Ability of the Platypus

Abstract

Reports of the underwater endurance of the platypus differ. In the present study, most dives observed at Melbourne Zoo were less than 3 min, but several were longer (up to 11 min). Calculated dive: surface ratios were between 2.5:1 and 20:1. Most dives in the laboratory were between 30 s and 4 min duration, and heart rate fell in all dives, from pre-dive rates of 140-230 to 10-120 beats min-1. These falls in heart rate indicate that blood supply to many tissues is restricted, but the short recovery times after dives suggest there is little anaerobic metabolism. Similarly, the distribution and properties of LDH isozymes in skeletal muscle do not suggest heavy dependence on anaerobic glycolysis, and the ability of platypus muscles to 'buffer' metabolic acids that accumulate during anaerobiosis is low relative to other diving mammals. The platypus dives after a large inspiration (about 50 mL for a 1-kg animal). Total blood volume of the platypus is not known, but haematocrit, haemoglobin concentration and oxygen-carrying capacity have been shown to be high. Myoglobin oxygen stores in platypus are about 5 mL per kg body weight. Estimates of available oxygen stores and oxygen consumption rate indicate little need for anaerobic metabolism during normal dives, and it is suggested that the platypus has the physiological capacity for greater underwater endurance than previously suggested.