Aquatic Gas Exchange in the Freshwater/ Land Crab, Holthuisana Transversa

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Abstract
Holthuisana transversa (von Martens), a freshwater/land crab from arid areas of Australia, is an efficient bimodal breather. In water, resting MO2 (1.65μmol g−1h−1) and Vm (15.6ml g−1 h−1) at 25°C were lower than in other aquatic crabs whilst percentage extraction of oxygen was quite high (47 %). MO2 was not regulated at low ambient PO2 but could be increased at least three times during exercise. Normoxic PaO2 was low (18 Torr) compared with other water-breathing crabs. The haemolymph contained haemocyanin which had a moderate affinity for oxygen (P50 = 8.0 Torr) and carried over 90% of the oxygen transported. Oxygen content of post-branchial haemolymph was low (346μmoll−1). There was a small positive Bohr shift (log P50/pH-0.33). The strategy of gas exchange in water is discussed and compared with that of aquatic crabs.