Fig. 1. (A–D). Wire frame plots of calculated intracellular PO2 (kPa) in slow oxidative fibres of the locomotory (pectoral) muscles from Antarctic notothenioid species. PO2 is on the vertical axis and fibre radius (µm) on the horizontal axes, with the centre at (0,0). The highest PO2 value (6 kPa) represents that of capillaries around a fibre; this declines both radially and circumferentially, initially with a steep gradient that quickly levels out towards the inner part of the fibre. The integrated response of differences in fibre size and intracellular compartments is predicted to maintain a similar level of tissue oxygenation at a cell temperature of 0°C when fibre radius is small. When fibre girth is increased, the decrease in mean PO2 is pronounced, an effect that is accentuated within the fibres of the channichthyid Chaenocephalus aceratus, where anoxic regions are predicted to occur. See text for details.