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We report measured concentrations of organohalogens and trace elements in muscle and eggs of returning wild Pacific sockeye and chinook salmon during their 2007 migration through the Fraser River watershed in Canada. Chemical analyses revealed the presence of ppb to ppm levels of a wide variety of contaminants in these fish, including polychlorinated biphenyls (PCBs); polychlorinated dibenzo-p-dioxins (PCDDs); polychlorinated dibenzofurans (PCDFs); polybrominated diphenyl ethers (PBDEs); organochlorine pesticides (OCPs) such as DDTs, hexachlorocyclohexanes (HCHs), octachlorostyrene, and cyclodienes; and Hg, As, Cd, Pb, and several other trace elements. Body weights and flesh lipid contents declined during upstream migration, resulting in significantly higher (p < 0.05) lipid-normalized concentrations of lipophilic organohalogens (PCBs, PCDD/Fs, pesticides) in those spawning salmon. Postmigration magnification factors (MFs) of organohalogens (0.1-10) were comparable to previous observations and model predictions. MFs generally increased with increasing hydrophobicity (K(OW)). For example, MFs of tetra- and pentachlorobenzenes and HCH isomers (log K(OW) range: 3.8-5) were relatively low (between 0.1 and 1.7) compared with those of more lipophilic compounds (log K(OW) > 6) such as PCBs, DDTs, and mirex (MFs between 5 and 10). Lipid-normalized muscle:egg ratios in female salmon, which varied between 0.1 and 8, also exhibited a positive relationship with chemical K(OW). The results indicate that lipophilic compounds (K(OW) > 10(6)) can be magnified in flesh lipids of Pacific salmon during spawning migration, but maternal transfer kinetics (deposition to eggs) of those chemicals are relatively slow compared with less hydrophobic compounds. 2,3,7,8-TCDD toxic equivalents (ΣTEQs) in eggs of these spawning salmon, calculated using WHO toxic equivalency factors (WHO-TEFs) for fish health, in some cases exceeded the 0.3 pg·g(-1) threshold level associated with 30% salmonid egg mortality, indicating the potential for reproductive impacts in Fraser River salmon populations.

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The health and physiological condition of anadromous salmon is of concern as their upriver migration requires navigation of human-impacted waterways and metabolism of stored energy reserves containing anthropogenic contaminants. Such factors may affect reproductive success of fish stocks. This study investigates chemical contaminant burdens and select gene expression profiles in Pacific Sockeye (Oncorhynchus nerka) and Chinook (Oncorhynchus tshawytscha) salmon which traverse the Fraser River watershed during their spawning migration. Chemical analyses of muscle tissue and eggs of salmon collected from the lower Fraser River (pre-migration) and from upstream spawning grounds (post-migration) during the 2007 migration revealed the presence of numerous chemical contaminants, including PCBs, dioxins/furans, pesticides, and heavy metals. However, muscle tissue residue concentrations were well below human health consumption guidelines and 2,3,7,8 TCDD toxic equivalents (SigmaTEQs) in salmon eggs, calculated using WHO toxic equivalency factors (WHO-TEFs) for fish health, did not exceed the 0.3pgg(-1) wet weight toxicological threshold level previously associated with 30% egg mortality in salmon populations. Quantitative real-time PCR probes were generated and used to assess differences in abundance of key mRNA transcripts encoding nine gene products associated with reproduction, stress, metal toxicity, and exposure to environmental contaminants. Gene expression profiles were characterized in liver and muscle tissue of pre- and post-migration Sockeye and Chinook salmon. The results of stock-matched animals indicate that dynamic changes in mRNA levels occur for a number of genes in both species during migration and suggest that Sockeye salmon exhibit a greater level of biological stress compared to the Chinook salmon population. Using a male-specific genotypic marker, we found that out of the 154 animals examined, one Sockeye was genotypically male but phenotypically female. This individual's gene expression profile in liver and muscle was reminiscent of, but not identical to, the female expression profile. These studies provide the first glimpse of the dynamic yet common nature of changes in the transcriptome that are shared between species during in-migration and highlight differences that may relate to population success. Continued longitudinal assessment will further define the association between contaminant burden, physiological stress, and modulation of gene expression in migrating Pacific salmon.

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