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To better understand the mechanisms that lead to marine mortality of homing adult sockeye salmon (Oncorhynchus nerka), gill and blood biopsies were used in combination with biotelemetry to demonstrate how survival to freshwater entry is related to gene expression and physiological indices of stress. Microarray analysis of gene expression indicated multiple biological processes, including immune and stress responses, protein biosynthesis, and metabolism. Quantitative reversetranscriptase polymerase chain reaction (qRT-PCR) analysis indicated fish with upregulation of genes related to stress and infection had higher marine survival compared with fish without this genomic signature. We proposed that higher marine survival of potentially stressed and immune compromised fish can be explained by stressed and infected fish being highly motivated to enter fresh water, leading to enhanced marine survival. However, once in a river, stressed and immune compromised fish could suffer higher mortality because of premature river entry. Overall, this study supports the idea that infection and stress are important biological processes influencing behaviour and fate of sockeye salmon during homing migrations. Pour mieux comprendre les mecanismes dont decoule la mortalite en mer de saumons rouges (Oncorhynchus nerka) adultes en migration de retour, des biopsies de branchies et de sang ont ete utilisees de concert avec la biotelemetrie pour etablir comment la survie jusqu'a l'entree en eau douce est reliee a l'expression genique et a des indices physiologiques du stress. L'analyse de l'expression genique a l'aide de biopuces fait ressortir plusieurs processus biologiques, dont des reactions immunitaires et de stress, la biosynthese de proteines et le metabolisme. L'analyse qRT-PCR indique que les poissons presentant une regulation positive des genes associes au stress et a l'infection ont un taux de survie en mer plus eleve que les poissons ne presentant pas cette signature genomique. Nous proposons que la plus grande survie en mer de poissons potentiellement stresses et immunocompromis peut s'expliquer par le fait que les poissons stresses et infectes seraient plus motives a entrer en eau douce, ce qui se traduirait par un taux de survie en mer plus grand. Une fois en riviere, cependant, les poissons stresses et immunocompromis pourraient avoir une plus forte mortalite en raison de leur entree prematuree en riviere. Globalement, les resultats de l'etude appuient la notion voulant que l'infection et le stress soient d processus biologiques qui influencent le comportement et le destin des saumons rouges durant leurs migrations de retour. [Traduit par la Redaction], Introduction Anadromous salmonids (from Salmo, Oncorhynchus, and Salvelinus genera) migrate from ocean feeding grounds to fresh water to reproduce, during which migrants undergo extensive physiological shifts associated with reproductive maturation [...]

Coastal commercial fisheries targeting Pacific salmon inevitably capture a mix of co-migrating species and genetically distinct populations within each species, only some of which are sufficiently abundant to sustain exploitation. Species-specific release measures are implemented as a conservation measure, but there remains little understanding of the resulting mortality. A purse seine fishery for Pacific salmon in British Columbia, Canada, was simulated with the goal of estimating post-release mortality for coho salmon, a species commonly released from commercial fisheries. Landed coho salmon (n = 220) were tagged with acoustic transmitters and tracked along their coastal approach and into freshwater. Survival analyses accounting for variable migration pathways among populations revealed population-specific survival, with the population of greatest conservation concern having the best survival. Condition assessments revealed scale loss to be the strongest predictor of success. Physically exhausted fish, identified via reflex impairment tests, also experienced higher mortality. Results highlight the complexity of estimating release mortality in mixed-population commercial fisheries and are discussed in the context of management implications. [ABSTRACT FROM AUTHOR]

We examined the effects of a commonly used preservation technique on mercury concentration in fish tissue. After fixing fish muscle tissue in formalin followed by preservation in isopropanol, we found that mercury concentration in fish muscle tissue increased by 18%, reaching an asymptote after 40 days. We used formalin–isopropanol-preserved longear sunfish ( Lepomis megalotis) from the Sam Noble Oklahoma Museum of Natural History to examine historical changes and predict current mercury concentrations in fish from two rivers in southeastern Oklahoma. Glover River was free-flowing, while Mountain Fork River was impounded in 1970 and a coldwater trout fishery was established upstream from the collection site in 1989. Mercury concentrations in longear sunfish from Glover River showed no historical changes from 1963 to 2001. Mercury concentrations in longear sunfish from Mountain Fork River showed no change from 1925 to 1993 but declined significantly from 1993 to 2003. We also compared mercury concentrations of the most recently collected longear sunfish in the museum to mercury concentrations of unpreserved fish collected from the rivers in 2006. Concentrations of mercury in museum fish were not significantly different from mercury concentrations in unpreserved fish we collected from the rivers. Our study indicates that preserved museum fish specimens can be used to evaluate historical changes and predict current levels of mercury contamination in fish. [ABSTRACT FROM AUTHOR]