Thermal acclimation and its reversal in early life stages of brook trout

In juvenile and adult fishes, the initiation, completion, and reversal of acclimation have been studied but there are few data on the dynamics of acclimation in early life stages. We examined how chronic warming during incubation altered thermal tolerance in early life stages of brook trout ( Salvelinus fontinalis) to quantify the scope and duration of thermal acclimation and carryover effects during early development. We assessed how quickly the acclimation of upper thermal tolerance (CT max ) was lost once hatched larvae were moved to common conditions. In embryos, and 4 weeks after hatch, fish in warmer treatments had a positive acclimation response (higher CT max ). Eight weeks after hatch, acclimation was completely reversed, whereby fry that had been reared in ambient (cooler) conditions had higher thermal tolerance than those from warm treatments. Early life stages of brook trout can acclimate their thermal tolerance throughout development but acclimation to warmer temperatures can have a cost in the form of lower body condition.