Microbial pathogens (bacteria, viruses, and microparasites) may cause impairment depending on the condition, age, and sex of the infected individual. Currently, little is known about disease in migrating salmon, and how disease profiles change as fish move from fresh to salt water. This is particularly true for anadromous salmonids such as Arctic charr (Salvelinus alpinus), who make annual migrations from overwintering in fresh water lakes to the marine environment for 6-8 weeks of feeding every summer. When these fish exit fresh water, they must completely change their osmoregulatory system from one that attempts to sequester salts in fresh water to one that expels salts and prevents their entry in to the blood stream in the marine environment. While undergoing this demanding transition, the surrounding microbial environment may also change, altering infection dynamics in a way that may be energetically costly to the migrating individual.
There is currently little information regarding the types of microbes that are present in Arctic charr populations in Canada, and there is no information on how infection properties may influence migration behaviour and success.
To provide the first survey of microbial pathogens in Arctic charr, and to explore relationships between pathogens and fish migration behaviour, PhD students Jacqueline Chapman and Robert Lennox, and MSc student Daniel Struthers travelled to Cambridge Bay, NU to work on char in the Grenier Lake system. Fish were collected by rod and reel, a small gill
sample was taken, and a V7 acoustic tag was externally attached to track the up-river migration using 16 VR2W Vemco acoustic receivers. While fish numbers were lower than anticipated, with the help of Inuit guides and long days fishing, the team was able to tag 14 charr and biologically sample over 40 fish from both the marine and freshwater environments.
Jacqueline will be taking the gill samples to the Pacific Biological Station in Nanaimo, BC this winter to run assays using high-throughput dynamic micro-array qPCR. Through this, she will quantify and compare RNA loading of microbes and changes in immune and osmoregulation gene expression in the marine and freshwater environment. Results from this field season will help researchers understand the ecological and evolutionary pressures associated with disease and seasonal feeding migrations of Arctic charr. Information garnered from the 2015 field season will further be used to inform upcoming research, which will involve experimental manipulation of fish stress and water temperatures to investigate how climate warming and fisheries interactions may influence Arctic charr immune function, pathogen loads, and ultimate survival.
This work is crucial given the importance of Arctic charr as a food source for subsistence and commercial fisheries in the North. Furthering our understanding of factors that influence charr population stability and survival, particularly in the face of climate warming, is key to sustainable management of this resource.