Absence of respiratory acclimation to diurnally-cycling temperature conditions in rainbow trout

1.Oxygen consumption and several ventilatory and cardiac functions were measured in rainbow trout normoxically acclimated to constant temperature conditions (2°, 10°, 18°C) or to a diurnal sinewave temperature cycle (10±4°C). The former groups were also exposed to a single ±4°C cycle. 2.No evidence of diurnal variation in respiratory activity was apparent, and this probably reflects the sampling schedule employed rather than absence of circadian rhythmicity. 3.Temperature related increases in oxygen consumption were closely correlated with increases in ventilatory rate, flow and stroke volume. The latter were associated with increases in pressure generation by buccal and opercular pumps. 4.Heart rate increased with temperature, and electrocardiogram records suggest that this may have been accompanied by increased cardiac output. 5.Enhanced oxygen utilization at higher temperature may stem from lamellar flow adjustments leacling to increases in effective branchial area. 6.There was no evidence of acclimation to cycling temperature conditions per se.