| Summary: | Gyrodactylus salaris is a salmon parasite, described for the first time in Sweden in the 1950s, occurring naturally also in Russia and Finland. During the 20th century it was broadly introduced to other countries in Europe. Reasons are for example introduction of farmed fish in natural rivers or the spread of parasites directly from fish farms into riverine systems. G. salaris can cause lethal diseases in entire salmon populations of a river as was seen in Norway in the 1970s. This thesis is based on the principle of a scoping review and aims to give an idea of a possible risk of dispersal of G. salaris into riverine systems by creating new spawning grounds for salmon within river restoration projects. The research site Kungsbackaån in Sweden is described and importance of river restoration to create natural spawning grounds for salmon is highlighted. In conclusion, a spread of G. salaris can be mitigated by precautionary actions and a removal of migration barriers is favorable for the development of natural spawning anadromous fish populations. If the parasite is once introduced into an ecosystem, eradication is difficult. Eradication methods used so far can cause significant damage to the ecosystem. It can be assumed that genetical features of salmon populations on the Swedish west coast are the main reasons for the fact that no devastating G. salaris outbreaks have yet been detected in that region. Further research is needed regarding the parasite G. salaris and its characteristics such as transmission routes or the parasite-host interaction, as well as environmental conditions impacting the development of parasite populations. It is particularly important to investigate the role of genetic differences in the host and parasite populations in the future.
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