Molecular assessment of parasite infection within socioeconomically important UK salmonid populations

Salmo trutta (Brown trout) is a native salmonid species to the United Kingdom. The economy generated via fish farming and eco-tourism has aided isolated communities in job creation and tourism income. It is particular true in highland communities in Scotland, where parasite infection has threatened the health of Scottish salmonids. The work presented in this thesis assessed parasite infection of wild brown trout populations in the northwest highlands of Scotland. Initial analysis of fish health screened subpopulations within the Gairloch region for infective parasite species. Eye fluke Diplostomum spp. was highly prevalent throughout the system with all lochs populations harboring infection. Through molecular analysis the species was confirmed as D. baeri which, when compared to other European isolates indicated highly diverse species complex infecting freshwater fish across the continent, most likely through definitive bird host. A cestode species that infected 4 trout subpopulations across the system was the medically relevant Diphyllobothrium dendriticum. Using molecular species identification techniques, it was the first finding of the parasite within UK freshwater fish populations. In response to differential parasite infection adaptive immunogenic traits were also observed within trout host subpopulations. The MHC II related gene Satr-DAB variability was higher in populations with differential parasite species infection suggesting the diversity of infection maintains MHC diversity within the population. The evasion of immune recognition to achieve high levels of infection is key to sustained parasite infection. The highly infective parasite in the Gairloch system, D. baeri, utilizes intracellular antigens Tetraspanins and Venom allergen-like antigenic proteins. These antigens were isolated using genomic techniques to highlight potential vaccine targets in aquaculture. The body of work presented here has furthered the knowledge of the highly infective D. baeri and provided molecular methodologies to identify medically relevant D. dendriticum. Genomic analysis of trout population immunogenics and parasite antigenic factors provides key knowledge to further conservation stocking methods and sustainable aquaculture practice.