Time course studies are critical for understanding regulatory mechanisms and temporal constraints in ectothermic animals acclimating to warmer temperatures. Therefore, we investigated the dynamics of heart rate and its neuro-humoral control in rainbow trout ( ITALIC! Onchorhynchus mykissL.) acclimating to 16°C for 39 days after being acutely warmed from 9°C. Resting heart rate was 39 beats min(-1)at 9°C, and increased significantly when fish were acutely warmed to 16°C ( ITALIC! Q10=1.9), but then declined during acclimation ( ITALIC! Q10=1.2 at day 39), mainly due to increased cholinergic inhibition while the intrinsic heart rate and adrenergic tone were little affected. Maximum heart rate also increased with warming, although a partial modest decrease occurred during the acclimation period. Consequently, heart rate scope exhibited a complex pattern with an initial increase with acute warming, followed by a steep decline and then a subsequent increase, which was primarily explained by cholinergic inhibition of resting heart rate.
Keywords: Acclimation dynamics; Cholinergic tone; Heart rate scope; Intrinsic heart rate; Maximum heart rate; Time course.
© 2016. Published by The Company of Biologists Ltd.