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The article presents a study which investigated the infection rate caused by Gyrodactylus salaris in juvenile Atlantic salmon in the Baltic Sea. It states that a DNA analysis of parasite specimens were sequenced for mitochondrial DNA (mtDNA) which were compared to variable nuclear marker sequences for clarification of isolated parasite strain genetic relationships with other strains. It cures the need to determine whether triploid Atlantic salmon are generally more susceptible to Gyrodactylus infection compared to their diploid counterparts regardless of their origin.

Genetic homogenization has been recognized as a serious threat in an increasing number of species, including many salmonid fishes. We assessed the rate and impact of immigration from the main hatchery stocks of Atlantic salmon in the Gulf of Bothnia into one of the largest wild salmon populations in the Baltic Sea, the River Vindelälven, within a temporal framework of 18 years (from 1985–2003). We provide genetic evidence based on mtDNA and microsatellite markers, using mixed-stock analysis, that a large proportion (66%) of fin-damaged spawners (n=181) caught in the Ume/Vindelälven during 1997–2003 originated from the hatcheries in the Rivers Ångermanälven, Luleälven and Ljusnan. The maximum-likelihood estimate of immigration rate from these hatcheries into the wild Vindelälven population was 0.068 (95% CI 0.021–0.128) over the studied time period (1985–2003) and reached up to a quarter (m=0.249, 95% CI 0.106–0.419) of the total population during 1993–2000. This resulted in significant (P<0.01) genetic homogenization trend between the wild Vindelälven population and hatchery stocks of the Ångermanälven and Luleälven. Our results demonstrate extensive straying from geographically distant hatchery releases into wild salmon population and emphasize the genetic risks associated with current large-scale stocking practices in the Baltic Sea.Heredity (2005) 95, 76–83. doi:10.1038/sj.hdy.6800693 Published online 4 May 2005 [ABSTRACT FROM AUTHOR]

The founder event in a recently recolonized salmon population in the Baltic Sea (Gulf of Finland) was investigated. To identify the origin of the founders, four wild populations and two hatchery stocks were analysed using six microsatellite loci. The results of assignment tests and factorial correspondence analysis suggest that the initial recolonizers of the river Selja originated from the geographically nearest (7 km) wild population (river Kunda) but as the result of stocking activities, interbreeding between recolonizers and hatchery individuals has occurred in subsequent years. Although the hatchery releases are out-numbering the wild salmon recruitment in the Baltic Sea at present, our results suggest that the native populations may still have an important role in colonization processes of the former salmon rivers. [ABSTRACT FROM AUTHOR]