In situ cardiac performance of Atlantic cod (Gadus morhua) at cold temperatures: Long-term acclimation, acute thermal challenge and the role of adrenaline

Abstract

The resting and maximum in situ cardiac performance of Newfoundland Atlantic cod (Gadus morhua) acclimated to 10, 4 and 0°C were measured at their respective acclimation temperatures, and when acutely exposed to temperature changes: i.e. hearts from 10°C fish cooled to 4°C, and hearts from 4°C fish measured at 10 and 0°C. Intrinsic heart rate (fH) decreased from 41 beats min-1 at 10°C to 33 beats min-1 at 4°C and 25 beats min-1 at 0°C. However, this degree of thermal dependency was not reflected in maximal cardiac output (Qmax values were ∼44, ∼37 and ∼34 ml min-1 kg-1 at 10, 4 and 0°C, respectively). Further, cardiac scope showed a slight positive compensation between 4 and 0°C (Q 10=1.7), and full, if not a slight over compensation between 10 and 4°C (Q10=0.9). The maximal performance of hearts exposed to an acute decrease in temperature (i.e. from 10 to 4°C and 4 to 0°C) was comparable to that measured for hearts from 4°C- and 0°C-acclimated fish, respectively. In contrast, 4°C-acclimated hearts significantly out-performed 10°C-acclimated hearts when tested at a common temperature of 10°C (in terms of both Qmax and power output). Only minimal differences in cardiac function were seen between hearts stimulated with basal (5nmol l-1) versus maximal (200nmol l-1) levels of adrenaline, the effects of which were not temperature dependent. These results: (1) show that maximum performance of the isolated cod heart is not compromised by exposure to cold temperatures; and (2) support data from other studies, which show that, in contrast to salmonids, cod cardiac performance/myocardial contractility is not dependent upon humoral adrenergic stimulation. © 2012. Published by The Company of Biologists Ltd.