CIRCADIAN-RHYTHM OF OXYGEN-CONSUMPTION AND OXYGEN LEVELS IN THE MUSCLE OF NOTOTHENIA-NEGLECTA (PISCES, TELEOSTEI)

1. The oxygen consumption of Notolhenia neglecta (Pisces, Teleostei) was measured during the Antarctic summer (16hr light and 8 hr twilight), in a sealed jar system. 2. Specimens of 917.5 g mean weight and of 34.2 cm mean standard length were used. 3. The oxygen levels in the muscle were continuously recorded by means of an oxygen microelectrode. 4. The behavior was observed by direct monitoring. 5. Different times were chosen for the measurements during the 24 hr of the day, at the temperature of 0°C. 6. The oxygen consumption was more or less constant during the morning, with a decrease in the late afternoon, corresponding to the highest point of the oxygen level in the muscle, to a marked decrease in activity. 7. At 8 a.m., another peak in the muscle oxygen level was observed, as well as the highest swimming activity and the highest susceptibility to gradual anoxia. 8. The values of respiratory frequency did not show a marked rhythmical variation. 9. Oxygen consumption, but mainly muscle oxygen levels and swimming activity, seem to have a circadian rhythm, as similar shaped curves repeated at different days and for different individuals. © 1990.