1. 1.

    Within a few hours of the lobsters being placed in the experimental chamber in normoxic water (Po2, 130-135 mmHg), their heart rate, oxygen uptake (Vo2) and ventilation volume (Vu) were relatively high. The scaphognathites were simultaneously active on both sides (bilateral ventilation) for 50% of the time, active on one side only (unilateral ventilation) for 32% of the time and simultaneously inactive (respiratory pause) for 18% of the time. Percentage extraction of O2 (% Ext.) was relatively low. 48h after having been set up, heart rate, VO2 and Vg had decreased significantly, % Ext. had increased and bilateral ventilation occupied 25% of the time. Heart rate was low and the beat irregular.

  2. 2.

    Upon subsequent exposure to hypoxia (PO2, 50-55 mmHg), Pa, O2, fell, there was initial hyperventilation, bilateral ventilation for 89% of the time, heart beat was more regular but Vo2 did not change significantly. An initial increase in pHa caused the O2 affinity of the Hey to rise. After 72h exposure to hypoxia Vg and pHa had declined, but Vg was still higher than at the end of the period of normoxia. Blood lactate, Vo2 and % Ext. were not significantly different from the values recorded after 48 h in normoxic water. Upon return to normoxic water, Vg and the time the animals spent ventilating both branchial chambers fell, but Vo2 increased.

  3. 3.

    It is concluded that for settled lobsters, Vo2 could be maintained during moderate hypoxia by increasing Vg maintaining a regular heart beat, and at least initially by increasing the O2 affinity of the Hey.

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