Abstract
Cultured Atlantic salmon Salmo salar are of international socioeconomic value, and the process of domestication has resulted in significant behavioural, morphological, and allelic differences from wild populations. Substantial evidence indicates that direct genetic interactions or interbreeding between wild and escaped farmed Atlantic salmon occurs, genetically altering wild salmon and reducing population viability. However, genetic interactions may also occur through ecological mechanisms (e.g. disease, parasites, predation, competition), both in conjunction with and in the absence of interbreeding. Here we examine existing evidence for ecological and non-reproductive genetic interactions between domestic Atlantic salmon and wild populations and the potential use of genetic and genomic tools to resolve these impacts. Our review identified examples of genetic changes resulting from ecological processes, predominately through pathogen or parasite transmission. In addition, many examples were identified where aquaculture activities have either altered the selective landscape experienced by wild populations or resulted in reductions in population abundance, both of which are consistent with the widespread occurrence of indirect genetic changes. We further identify opportunities for genetic or genomic methods to quantify these impacts, though careful experimental design and pre-impact comparisons are often needed to accurately attribute genetic change to aquaculture activities. Our review indicates that ecological and non-reproductive genetic interactions are important, and further study is urgently needed to support an integrated understanding of aquaculture-ecosystem interactions, their implications for ecosystem stability, and the development of potential mitigation and management strategies.
Highlights
Atlantic salmon Salmo salar aquaculture is of international socioeconomic importance, and the processPublisher: Inter-Research · www.int-res.comAquacult Environ Interact 12: 429–445, 20202011, Wringe et al 2019) differences from wild popu- where hybridization with escapees is not common or lations
Several studies have documented the spread of furunculosis, a septicemic bacterial disease, from fish farms to wild salmonids in Norwegian rivers (Johnsen & Jensen 1994). These findings indicate that ecologically induced genetic impacts on wild salmon populations associated with disease transmission from aquaculture populations are highly likely
Zueva et al (2018) compared salmon populations from northern Europe classified as extremely susceptible or resistant to G. salaris. They identify 57 candidate genes potentially under resistance-associated selection and this set of loci was shown to be enriched for genes associated with both innate and acquired immunity. These findings suggest that ecological and non-reproductive genetic impacts on wild populations associated with parasite transmission, such as sea lice from aquaculture installations, are highly likely, both because of the potential for substantial mortality to occur through exposure and for it to be selective through a clear genetic basis to population differences in resistance
Summary
Atlantic salmon Salmo salar aquaculture is of international socioeconomic importance, and the processPublisher: Inter-Research · www.int-res.comAquacult Environ Interact 12: 429–445, 20202011, Wringe et al 2019) differences from wild popu- where hybridization with escapees is not common or lations. There is substantial evidence that regarding the amplification of pests and pathogens direct genetic interactions, defined as interbreeding, such as sea lice through net pen aquaculture (e.g. occurs between wild Atlantic salmon and escaped do- Vollset et al 2016, Karbowski et al 2019), the potential mestic individuals Bolstad et al 2017, Bradbury et al 2020) Both in Can- lantic salmon and other species, the evidence for their ada and Norway, recent evidence suggests hybridiza- presence and our ability to quantify their magnitude tion may be extensive following escape events (Karls- has been limited to date (Verspoor et al 2015)
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