Octopus vulgaris is able to maintain its oxygen uptake at a steady level down to a POO2 of below 80 mmHg. This capacity is scarcely affected by surgical reduction of the gill area to between 30 and 50%, a finding which confirms previous work suggesting that regulation is achieved by increasing the affinity of the haemocyanin rather than by circulatory adjustments. The same reductions in gill area seriously reduce the already very limited metabolic scope of Octopus. Experiments in an exercise wheel show that this is in the region of 115 ml kg−1h−1 (against an SMR of 42 for a 1-kg animal at 21 C) in the intact Octopus; reduction of the gill area to 30–50% approximately halves this figure. Animals with their gills reduced will run in the wheel until they have accumulated an oxygen debt in the region of 22ml kg−1, and then stop; recovery is slower than in intact animals.

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