| Summary: | In teleost fish, the microbiome plays a variety of roles in host physiology and adaptability to different environments. Anadromous fish (migrating to sea after maturation and returning to freshwater to spawn) are reported to experience turnover of their bacterial communities when transitioning between marine and freshwater environments. Microbiomes of Arctic salmonids are poorly studied, and cold-water environments may support colonization by different microbes. Additionally, anadromous Arctic salmonids perform seasonal migrations, escaping super-cooled seawater in winter. Therefore, it is of interest to determine if these fish experience repeated seasonal recolonizations. This thesis attempts to further understanding of Arctic salmonid microbiomes in two investigations. In the first investigation, anadromous Arctic char (Salvelinus alpinus) from the Kitikmeot region, Nunavut, were sampled and bacterial communities from the intestine characterized using 16S rRNA gene fragment analysis. Bacterial communities were compared across seasonal habitats within the char’s migration route. Communities showed differences between brackish and freshwater habitats, and between different temporal stages of freshwater residence. Brackish communities were broadly consistent with taxa seen in other anadromous salmonids, but were rich in psychrophiles at the genus level, including a putative symbiote, Photobacterium iliopiscarium occurring in >90% of fish from brackish waters. Freshwater communities were more variable and less consistent taxonomically with other salmonids, possibly reflecting char’s winter fasting behaviour. These results suggest that climate change could affect relationships between Arctic char and their symbiotes. In the second investigation, intestinal communities of lake whitefish (Coregonus clupeaformis) were compared to char, with which they were sympatric and behaving anadromously. Lake whitefish appeared to experience similar community shifts with salinity, but community composition was significantly different from char, and at freshwater sites appeared to be more affected by geography. Lake whitefish communities were generally more diverse than in char and appeared to be more represented by groups known to contain opportunistic pathogens. Additionally, community diversity was more affected by feeding than in char. Together, the results suggested that lake whitefish in this environment, which is at their northern limit, exercise less selection on their intestinal communities than char, and this could reflect their on-going evolutionary adaptation to high Arctic microbes. M.Sc.
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