The Effects of Elevated Water Temperature on Adult Sockeye Salmon Blood Properties and Gene Expression

Peak summer temperatures in the Fraser River, B.C., Canada, have increased ~2ºC in the past 60 years with several of the warmest years on record occurring within the past 20 years. Peak summer temperatures are expected to increase another 2ºC by the end of the century. Elevated river water temperatures have been associated with higher en route and prespawn mortality in Pacific salmon; however the mechanisms of mortality remain unknown. We collected wild sockeye salmon and exposed them to different temperature treatments in a controlled laboratory environment to evaluate the effect of water temperature on gill tissue gene expression, blood physiology and body energy stores. Fish were live sampled before and during the temperature exposure period (5 days at 19°C or 13°C) to evaluate how water temperature affects gill tissue and blood plasma properties. Using cGRASP 32K gene cDNA microarrays, it is possible to determine what biological pathways are affected in fish exposed to environmental stressors. We will compare gill tissue gene expression profiles from fish held at 19°C to fish held at 13°C to determine which biological pathways are affected by high water temperature. Fish held at 19°C had increased mortality and significantly higher plasma chloride and osmolality compared to fish held at 13°C, which suggests that 19°C represented a stressful temperature. As fish died, muscle chunks were taken to determine the effects of the temperature treatments on muscle energy stores. We will attempt to demonstrate the effects of elevated water temperature on adult sockeye salmon at multiple levels of biological organization. These results will provide insight into the consequences of exposure to high water temperatures on adult sockeye salmon during spawning migrations.