Rapid cardiac thermal acclimation in wild anadromous Arctic char (Salvelinus alpinus)

Abstract

Migratory fishes commonly encounter large and rapid thermal variation, which has the potential to disrupt essential physiological functions. Thus, we acclimated wild, migratory Arctic char to 13°C (∼7°C above a summer average) for an ecologically relevant period (3 days) and measured maximum heart rate (ƒH,max) during acute warming to determine their ability to rapidly improve cardiac function at high temperatures. Arctic char exhibited rapid compensatory cardiac plasticity similar to past observations following prolonged warm acclimation: they reduced ƒH,max over intermediate temperatures (-8%), improved their ability to increase ƒH,max during warming (+10%), and increased (+1.3°C) the temperature at the onset of an arrhythmic heartbeat, a sign of cardiac failure. This rapid cardiac plasticity may help migrating fishes such as Arctic char mitigate short-term thermal challenges. Furthermore, by using mobile Arctic research infrastructure in a remote field location, the present study illustrates the potential for field-based, experimental physiology in such locations.

Keywords: Acclimation rate; Cardiac function; Climate change; Heart rate; Thermal tolerance; Thermal variation.

Fig. 1.

River temperatures at Halokvik, NU, Canada, during research on the upriver Arctic char migration in 2013 and 2017. Data are presented as the daily mean (solid line), minimum and maximum (upper and lower shading).

Fig. 2.

The response of maximum heart rate (ƒ_H,max) to acute warming in wild adult Arctic char with and without (control) a 3 day warm acclimation (∼13°C). The mean (±s.e.m., shading) ƒ_H,max (A) and corresponding incremental Q₁₀ (B) are shown during acute warming in control (n=15) and warmed (n=9) fish, with dashed lines indicating temperatures at which individuals were excluded after exhibiting cardiac arrhythmias. Model statistics are presented in Table S1. The inset in A shows the progressive increase in the percentage of individual fish showing a cardiac arrhythmia at a supra-optimal temperature.

Fig. 3.

The effect of a 3 day warm acclimation on ƒ_H,max and transitional temperatures for ƒ_H,max during acute warming. Mean (±s.e.m.) and individual values (semi-transparent) are shown for (A) ƒ_H,max at 5°C, the peak ƒ_H,max and the difference between the two (Δƒ_H,max), and (B) the temperatures at which incremental Q₁₀ fell below 1.5 (T_Q10<1.5), peak ƒ_H,max occurred (T_peak) and the heart became arrhythmic (T_arr). P-values for the effect of warm acclimation (t-test) are presented above each metric with significant differences in bold.