Proteomic analysis of sockeye salmon serum as a tool for biomarker discovery and new insight into the sublethal toxicity of diluted bitumen.

Pipelines carrying diluted bitumen (dilbit) from Canada's oil sands traverse North America, including the freshwater habitat of Pacific salmon, posing a risk of environmental release and aquatic exposure. Swimming performance is impacted in juvenile sockeye (Oncorhynchus nerka) exposed to dilbit; therefore biomarkers of dilbit exposure will be valuable for monitoring at-risk salmon stocks. This study characterized changes in the serum proteome of sockeye exposed to a sub-lethal and environmentally relevant concentration of dilbit using isobaric tags for relative and absolute quantitation (iTRAQ), and included a range of experimental conditions to permit identification of biomarkers that are robust across time (1 and 4wk) and exercise level (at rest and following a swim test). Over 500 proteins were identified and quantified in sockeye serum, with dilbit exposure significantly altering the abundance of 24 proteins irrespective of time and exercise, including proteins associated with immune and inflammatory responses, coagulation, and iron homeostasis. An increase in creatine kinase (CK) activity in serum of dilbit-exposed salmon confirmed the higher CK protein abundance measured using iTRAQ. The combination of 4wk dilbit exposure and a swim test had a greater effect on the serum proteome than either treatment alone, including a marked increase in tissue leakage proteins, suggesting that aerobic exercise exacerbates the serum proteome response to dilbit, and the increased cellular damage could impede exercise recovery. This study provides a foundation for the development of bio-monitoring tools for salmon stock assessments, and offers new insights into the sub-lethal toxicity of crude oil exposure in fish.