Do prior diel thermal cycles influence the physiological response of Atlantic salmon (Salmo salar) to subsequent heat stress?

We designed two environmentally relevant thermal cycling regimes using monitoring data from an Atlantic salmon river to determine if exposure to prior diel cycles stimulated protective mechanisms (e.g. heat hardening), and/or resulted in physiological and cellular stress. Wild fish were exposed to three days of diel cycling in the lab and then exposed to an acute thermal challenge near their upper reported critical temperature. We measured routine metabolic rate across the time course as well as indicators of physiological status (e.g. plasma glucose and osmolality) and cellular stress (e.g. heat shock protein 70). We observed that thermal cycling altered physiological and cellular responses, compared to an acute heat shock, but saw no differences between cycling regimes. Unique temperature regime and tissue specific responses were observed in heat shock protein induction, metabolites, haematology and osmotic indicators. Routine metabolic rate was not affected by the thermal cycling and increased according to Q10 predictions. While we report unique physiological and cellular responses between all treatment groups, we did not observe a clear indication of a heat hardening response.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author