Echocardiography and electrocardiography reveal differences in cardiac hemodynamics, electrical characteristics, and thermal sensitivity between northern pike, rainbow trout, and white sturgeon.

Doppler and B-mode ultrasonography and electrocardiography (ECG) were used to determine cardiac hemodynamics and electrical characteristics in 12°C-acclimated and metomidate-anesthetized northern pike, rainbow trout and white sturgeon (7-9 per species) at 12°C and 20°C, and at a comparable heart rate (f , ~60 beats/min). Despite similar relative ventricle masses and cardiac output (Q), interspecific differences were observed at 12°C in f , ventricular filling and ejection, stroke volume, the duration ECG intervals, and cardiac valve cross-sectional areas. Vis-a-fronte filling of the atrium due to ventricular contraction was observed in all species. However, biphasic ventricular filling (i.e., due to central venous pressure and then atrial contraction) was only observed in rainbow trout and white sturgeon. Changes in atrial and ventricular performance varied between the species as temperature increased from 12°C to 20°C. Rainbow trout had the highest thermal sensitivity for f (Q  = 3.73), which doubled Q, and the largest increase in transvalvular blood velocity during ventricular filling. Conversely, northern pike had the lowest Q for f (1.58) and did not increase Q. At ~60 beats/min, the rainbow trout heart had the shortest period of electrical activity, which also resulted in the longest recovery period (TP interval) between successive beats. The QT interval at ~60 beats/min was also longer in the white sturgeon versus the other species. These results suggest that interspecific differences in fish cardiac hemodynamics may be related to cardiac morphology, the duration of electrical impulses through the heart, cardiac thermal sensitivity, and valve dimensions.