Abstract
A definite rhythm was observed in the bimodal oxygen uptake of the air-breathing siluroid fish, Clarias batrachus. The total oxygen uptake was at its peak (222.3±20.25 mlO2·kg-1·h-1) during dawn (04-06h), whereas the minimum oxygen uptake (63.68±5.14mlO2·kg-1·h-1) was recorded in the midday hours (12-14h). It seems that the rhythmic fluctuations in the metabolism of C. batrachus are related to the diurnal fluctuations of dissolved oxygen and free carbon dioxide in the swamps where this fish normally inhabits.
