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Diseases of Aquatic Organisms

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DAO 71:119-129 (2006)  -  doi:10.3354/dao071119

Identification of genetic markers associated with Gyrodactylus salaris resistance in Atlantic salmon Salmo salar

John Gilbey1,4,*, Eric Verspoor1,4, Tor Atle Mo2, Erik Sterud2, Kjetil Olstad2, 5, Sigurd Hytterød2, Catherine Jones3, Leslie Noble3

1Fisheries Research Services (FRS) Marine Laboratory, Victoria Road, Aberdeen AB11 9DB, UK
2National Veterinary Institute, PO Box 8156 Dep., 0033 Oslo, Norway
3University of Aberdeen, School of Biological Science, Department of Zoology, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
4Present address: FRS Freshwater Laboratory, Faskally, Pitlochry PH16 5LB, UK
5Present address: The Natural History Museums and Botanical Garden (NHM), University of Oslo, P.O. Box 1172, Blindern 0318 Oslo, Norway

ABSTRACT: Gyrodactylus salaris Malmberg, 1957 is a freshwater monogenean ectoparasite of salmonids, first recorded in Norway in 1975 and responsible for extensive epizootics in wild Atlantic salmon Salmo salar L. The susceptibility of different populations of Atlantic salmon to G. salaris infection differs markedly, with fish from the Baltic being characterised as relatively resistant whereas those from Norway or Scotland are known to be (extremely) susceptible. Resistance to Gyrodactylus infection in salmonids has been found to be heritable and a polygenic mechanism of control has been hypothesised. The current study utilises a ‘Quantitative trait loci’ (QTL) screening approach in order to identify molecular markers linked to QTL influencing G. salaris resistance in B1 backcrosses of Baltic and Scottish salmon. Infection patterns in these fish exhibited 3 distinct types; susceptible (exponential parasite growth), responding (parasite load builds before dropping) and resistant (parasite load never increases). B1 backcross fish were screened at 39 microsatellite markers and single marker-trait associations were examined using general linear modelling. We identified 10 genomic regions associated with heterogeneity in both innate and acquired resistance, explaining up to 27.3% of the total variation in parasite loads. We found that both innate and acquired parasite resistance in Atlantic salmon are under polygenic control, and that salmon would be well suited to a selection programme designed to quickly increase resistance to G. salaris in wild or farmed stocks.

KEY WORDS: Gyrodactylus salaris · Atlantic salmon · Resistance · Linkage mapping · Quantitative trait loci

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