1. Oxygen uptakes from air and water have been measured in relation to weight of the African lungfish Protopterus amphibius Peters. 2. Combined O2 uptake from air and water ranged from 60 ml O2 kg-1 h-1 STPD, in a 3-7 g specimen, to 30 ml O2kg-1 h-1, in a 255 g specimen. 3. While the combined O2 uptake changed by a factor of 2, within the weight range under study, the aquatic O2 uptake changed 8-fold within the same range. The smaller fish satisfy 70% of their O2 requirement by aquatic breathing compared to 10–15% in the grown specimens. 4. The pattern of bimodal breathing in P. amphibius is discussed in relation to the natural habitat of the species.

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