A heart to heart on temperature: impaired temperature tolerance of triploid rainbow trout (Oncorhynchus mykiss) due to early onset of cardiac arrhythmia.

Triploid (3N) salmonids are of interest to aquaculture and sport fishing industries, however it has been shown that 3N fish have impaired tolerance to high temperatures. To test the hypothesis that poor high temperature tolerance in 3N salmonids is related to impaired O2 delivery to the body, maximum heart rate (fH) was measured in 2N (diploid) and 3N rainbow trout (Oncorhynchus mykiss) during an incremental temperature challenge. fH of both ploidies was similar at 10°C. However, a significant effect of ploidy on the response of fH to temperature from 10 to 22°C was reflected in a lower Q10 for 3N individuals. Additionally, all 3N trout developed a cardiac arrhythmia by 22°C, where 30% of 2N trout continued to maintain a rhythmic heartbeat. These findings suggest that reduced 3N high temperature tolerance could be due to early collapse of the cardiovascular system's ability to deliver O2 to the body during warming.