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Impacts of Diluted Bitumen on Sockeye Salmon Physiology

The Southern Ontario L-SETAC Pub Night concluded the 2015-2016 season on Thursday, March 31st at the Shakespeare Arms in Guelph. Our speaker of the night was Dr. Sarah Alderman, a Post-Doctoral researcher at the University of Guelph, who conducted research on how exposure to diluted bitumen (dilbit) impacts the physiology of sockeye salmon (Oncorhynchus nerka). Pipelines carrying dilbit from the Alberta Oil Sands already traverse the coastal watersheds of British Columbia, and proposals to expand this infrastructure are under review, putting millions of Pacific salmon at risk of exposure to this known toxicant. Given that crude oils are cardiotoxic to fish, and that sockeye salmon depend on a healthy cardiovascular system to achieve two significant lifetime migratory events, Dr. Alderman’s research aims to discern the nature and extent of dilbit cardiotoxicity in sockeye at different life stages. Dr. Alderman exposed salmon embryos to environmentally relevant concentrations of the water-soluble fraction of dilbit, and then raised them to juveniles in clean water prior to conducting critical swimming speed tests in a controlled flume. While there were no latent effects on swimming performance in fish exposed to dilbit during development, acute exposure of juveniles had different results. One year-old sockeye parr exposed for four weeks to sub-lethal concentrations of dilbit (~65 mg L-1 total PAH) demonstrated elevated liver EROD activity and upregulation of ahr and cyp1A mRNA in the heart. Heart morphology was also altered in these exposed fish, with increased collagen content (fibrosis) in ventricle tissue relative to unexposed fish. Finally, these cellular and histological effects in the heart were associated with significantly reduced swimming performance in exposed fish. Dr. Alderman’s studies demonstrate that young salmon are sensitive to dilbit contamination, and that accidental discharge could have dramatic implications on these fish by impacting their ability to avoid predators as well as their migratory capacity. – Submitted by Gerald Tetreault

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