Intrinsic rates of heartbeat in Antarctic fishes: Is an icefish different?

Abstract

Between 1992 and 1994, temperature effects on cardiac pacemakers of three notothenioid fish species were investigated at Scott Base and Terra Nova Bay Station, Antarctica by recording electrical activity from isolated atria. Spontaneous rhythmic electrical activity correlated closely with visible contractions of the atrium. For the icefish Chionodraco hamatus, a mean rate of 15.2 ± 0.69 beats per minute (B/min) was recorded at 0°C, which agreed well with a mean pressure pulse frequency of 15.3 ± 0.42 B/min determined in vivo with a caudal arterial cannula. At the same temperature, slightly higher intrinsic rates of 23.5 ± 0.42 and 24.26 ± 0.88 B/min were measured in the red-blooded nototheniids Trematomus bernacchii and Pagothenia borchgrevinki, respectively. A bimodal distribution of rates was apparent in deteriorating preparations and fatigued low-frequency subpopulations were eliminated from further analysis. Linear regression confirmed that the atrial pacemaker is slower in C. hamatus but that temperature coefficients are similar for all 3 species: C. hamatus, f_H = 16.39 + 2.89 T; T. bernacchii, f_H = 24.55 + 2.69 T; P. borchgrevinki, f_H = 24.78 + 3.25 T, where f_H = heart rate, B/min and T = temperature, °C. The results appear to have predictive value for other antarctic fishes.