LAUSR

As poikilotherms, fish health is compromised by exposure to elevated temperatures (e.g. climate change-related warming, anthropogenic thermal pollution, and/or hatchery processes). While fish thermotolerance has been demonstrated to be plastic, the downstream impacts of early life-stage high temperature exposure are not known. In the present study, we investigated the thermotolerance of rainbow trout (Oncorhynchus mykiss) fry 2 months after being exposed to elevated temperature (22°C) for 96 h. Exposed fry demonstrated a reduced critical thermal maxima (CTmax) in comparison to control fish. Using the RNase H-dependent quantitative PCR method, expression of rainbow trout hsp70 isoforms was determined immediately after the acute thermal stress and immediately following the thermotolerance trials. The lowered CTmax was associated with a reduced ability to upregulate the hsp70b gene during the thermotolerance trials, whereas no changes in hsp70a were observed. Overall, these results indicate that exposure to thermal stress in early life-stages of rainbow trout can have negative effects on future physiological function.