Beat the heat: Physiological responses of Atlantic salmon to an ecologically relevant thermal challenge

Temperature has profound effects on the biology of fishes and climate change-mediated increases in water temperature are putting many Canadian species at risk.

The Miramichi River in New Brunswick is one of Canada’s largest runs of wild Atlantic salmon. In the last decade, temperatures recorded in the Miramichi River during the summer have exceeded those thought to represent the upper limit Atlantic salmon can tolerate.

These limits have been assessed using a standardized thermal challenge in the laboratory where fish are exposed to increases in temperature over relatively short periods of time.

We were interested to know if environmentally realistic fluctuations in water temperature, typical of a summer day in the Miramichi River, would be stressful for juvenile Atlantic salmon.

We used real-world temperature data collected from the Miramichi River to replicate river conditions in the laboratory. Fish were held in tanks and water temperature was gradually increased from 15°C to 26°C and then decreased back to 15°C over 34 hours.

Our first objective was to describe the cellular changes in juvenile Atlantic salmon before, during and following this ecologically relevant heat challenge.

We found that our heat challenge caused cellular stress as shown by increases in levels of Heat Shock Protein 70 in the heart, liver, muscle and blood. This protein increases in cells to offer protection from damaging heat stress.

Our second objective was to determine if this heat challenge would affect how fish responded to a second, more severe heat stress.

We found that fish in better condition had a higher thermal tolerance but a prior heat challenge had no effect on thermal tolerance in juvenile Atlantic salmon.

High water temperatures during the summer are implicated in the decline of wild Atlantic salmon in eastern Canada, and may result in the closing of recreational fisheries.

Our work highlights the importance of using environmentally realistic increases in water temperature to determine thermal limits of fishes and to provide insight into successful management and conservation strategies.

Read the full paper — Physiological responses to a short-term, environmentally realistic, acute heat stress in Atlantic salmon, Salmo salar
by Melanie J. Gallant, Sacha LeBlanc, Tyson J. MacCormack and Suzanne Currie.