High latitude, high tolerance: Northern juvenile Chinook salmon exhibit substantial thermal plasticity and acute heat tolerance

Warm acclimation substantially increases whole-organism heat tolerance in juvenile Yukon River Chinook salmon, including during swimming, across summer temperatures up to 22.5°C.

• Why it matters: Rising river temperatures and more frequent heat waves in the North threaten Alaska Chinook salmon, but the thermal sensitivity and acclimation capacity at the northern range edge remain unclear.
• What they did: Juvenile Yukon River Chinook were acclimated to 12.5, 15, 17.5, 20, or 22.5°C under 100% versus 40% satiation feeding, then tested for heat tolerance at rest and while swimming and for heart-rate and cardiac electrical thermal sensitivity.
• The result: Warm acclimation increased cardiac heat tolerance, reset maximum heart rate to lower levels, and shortened PR and QRS intervals while lengthening QT, suggesting AV conduction limits may constrain function at acute high temperatures.

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