Elevated cortisol lowers thermal tolerance but results in limited cardiac remodelling in rainbow trout (<i>Oncorhynchus mykiss</i>) experiencing chronic social stress

Juvenile rainbow trout (Oncorhynchus mykiss) held in pairs form dominance hierarchies which subordinate individuals experience chronic social stress accompanied by lowered thermal tolerance (assessed as the critical maximum, CTmax). Here we tested hypothesis that elevation of circulating cortisol levels reduces trout. In support this hypothesis, recovered from for 48 h, a period sufficient to return normal baseline levels, no longer showed reduced CTmax. Further, was not restored subordinates treated with during recovery stress. To explore possible mechanisms underlying effect on CTmax, also induces cardiac remodelling trout, previously reported cortisol-treated Ventricle mass and hypertrophy markers were unaffected Picrosirius red staining revealed trend lower collagen ventricles relative dominant However, type I transcript protein turnover unaffected. Indicators function, including ventricle passive stiffness intrinsic heart rate (fH), similarly vivo fH similar between fish. Nevertheless, keeping their fish exhibited arrhythmia at significantly temperatures than CTmax trials. Thus, high result tolerance, but 5 d did greatly affect structure function.