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Population genetic differentiation of sea lice (Lepeophtheirus salmonis) parasitic on Atlantic and Pacific salmonids: analyses of microsatellite DNA variation among wild and farmed hosts

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The copepod Lepeophtheirus salmonis is ectoparasitic on Atlantic and Pacific wild salmonids. It is a major pest to Atlantic salmon (Salmo salar) aquaculture and may be implicated in recent declines of certain European wild salmonid stocks. Variation at six microsatellite loci was assessed among L. salmonis from wild and farmed salmonids in Scotland, wild sea-run brown trout (Salmo trutta) in Norway, and farmed Atlantic salmon in eastern Canada. An outgroup North Pacific sample was obtained from farmed Atlantic salmon in British Columbia. No significant differentiation was found between L. salmonis from the host species or among samples from throughout the North Atlantic. This is consistent with long-distance oceanic migration of wild hosts and larval interchange between farmed and wild host stocks being sufficient to prevent genetic divergence of L. salmonis throughout the North Atlantic. These results have important management implications for both wild stock conservation and aquaculture in that genetically, L. salmonis in the North Atlantic comprises a single population: there is no evidence of isolation of populations on farmed hosts from those on wild fish. Comparison between North Pacific and North Atlantic L. salmonis populations showed significant but low differentiation (FST = 0.06).

Le copépode Lepeophtheirus salmonis est un ectoparasite des salmonidés sauvages de l'Atlantique et du Pacifique. C'est un ravageur important dans l'aquaculture du saumon de l'Atlantique (Salmo salar) et il est peut-être impliqué dans le déclin récent de quelques stocks sauvages européens. Nous avons évalué la variation à six locus microsatellites des L. salmonis chez des saumons en nature et en pisciculture en Écosse, des truites de mer sauvages (Salmo trutta) en Norvège et des saumons de l'Atlantique de pisciculture dans l'est du Canada. Un échantillon du Pacifique nord obtenu chez les saumons de pisciculture de la Colombie-Britannique a servi de groupe externe. Il n'existe aucune différence significative entre les L. salmonis, ni en fonction des hôtes, ni en fonction des échantillons, dans tout l'Atlantique nord. Cela s'explique par la migration océanique sur de grandes distances des hôtes sauvages; de plus, les échanges de larves entre les hôtes de stocks sauvages et cultivés suffisent à empêcher la divergence génétique chez L. salmonis dans tout l'Atlantique nord. Ces résultats ont d'importantes conséquences sur la gestion des stocks sauvages et des stocks de pisciculture, parce que les L. salmonis de l'Atlantique nord forment une seule population génétique; il n'y a aucune indication que les populations qui parasitent les hôtes de pisciculture soient isolées de celles qui vivent sur les poissons sauvages. Une comparaison des populations du Pacifique nord et de l'Atlantique nord montre une différentiation faible, mais significative (FST = 0,06).[Traduit par la Rédaction]

Document Type: Research Article

Publication date: July 1, 2004

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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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