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Parvicapsula minibicornis infections in gill and kidney and the premature mortality of adult sockeye salmon (Oncorhynchus nerka) from Cultus Lake, British Columbia

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Abstract:

In recent years, large losses of migrating adult sockeye salmon (Oncorhynchus nerka) from the Fraser River, British Columbia, Canada, have resulted in reductions in catches and productivity. We investigated patterns of mortality and the occurrence of the myxosporean parasite Parvicapsula minibicornis in adult sockeye salmon from Cultus Lake, tributary to the Fraser River. Using data from a captive broodstock program, we found that early migrants to Cultus Lake had less severe P. minibicornis infections and were more likely to survive to maturity than those fish that arrived later after they had presumably held in the warmer Fraser River. We found P. minibicornis in kidneys and gills of spawners. In some fish, significant histopathology in the gills that included severe inflammation and hyperplasia of the gill lamellae was observed; the severity of the disease was correlated with the severity of P. minibicornis infections. Kidney and gill pathologies were more prevalent and more severe in fish that died before spawning compared with those that matured successfully. Gill disease associated with P. minibicornis infections had not been previously identified in Fraser River sockeye salmon, and its role in the loss of spawners needs further investigation.

Ces dernières années, de lourdes pertes de saumons rouges (Oncorhynchus nerka) adultes migrateurs dans le fleuve Fraser, Colombie-Britannique, Canada, ont causé des réductions des prises et de la productivité. Nous examinons les patrons de mortalité et l’occurrence de la myxosporidie parasite Parvicapsula minibicornis chez les saumons rouges adultes du lac Cultus qui se déverse dans le fleuve Fraser. À l’aide de données provenant d’un programme impliquant un stock reproducteur captif, nous observons que les migrateurs précoces dans le lac Cultus ont des infections à P. minibicornis moins sévères et qu’ils sont plus susceptibles de survivre jusqu’à la maturité que les poissons qui arrivent plus tard après avoir vraisemblablement été retenus dans les eaux plus chaudes du fleuve Fraser. Nous avons trouvé P. minibicornis dans les reins et les branchies des reproducteurs. Nous avons observé chez certains poissons une importante histopathologie des branchies et, en particulier, une inflammation sévère et une hyperplasie des lamelles branchiales; la gravité de la maladie est en corrélation avec la sévérité des infections de P. minibicornis. Les pathologies des reins et des branchies sont plus fréquentes et plus graves chez les poissons qui sont morts avant la fraie, par comparaison à ceux qui ont frayé avec succès. On n’avait pas signalé auparavant la maladie des branchies associée à P. minibicornis chez les saumons rouges du fleuve Fraser et il faudra étudier plus au fond son rôle dans la perte des reproducteurs.

Document Type: Research Article

Publication date: 2010-04-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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