An example of the relationship between O2 uptake per breath and preceding apnoea duration for each fish at an aerial O2 partial pressure of 40 kPa. An example of the relationship between O2 uptake per breath and preceding apnoea duration for each fish at an aerial O2 partial pressure of 40 kPa. The slope represents aerial O2 consumption rate (ml min-1) during apnoea: Fish 1=0.0076; Fish 2=0.0069; Fish 3=0.0056; Fish 4=0.0051; Fish 5=0.0047; Fish 6=0.0033; Fish 7=0.0017. Lesley A. Alton et al. J Exp Biol 2007;210:2311-2319 © The Company of Biologists Limited 2007