Experiments to test if allopatric Salvelinus alpinus are suitable year-round hosts of Gyrodactylus salaris (Monogenea)

There has been an increased focus on Salvelinus alpinus as a potential long-term host to Gyrodactylus salaris and, here, both susceptibility to G. salaris and ability to sustain a parasite population seasonally, was tested using fry and parr of S. alpinus from the River Skibotnelva, northern Norway. Fry were highly susceptible. Gyrodactylus salaris survived on allopatric S. alpinus parr during the 5 month-long winter when water temperatures were c. 1° C. Salvelinus alpinus fry also maintained a pulse of G. salaris infection for over 155 days from early May until autumn. Gyrodactylus salaris are thus able to reproduce and survive on S. alpinus for long periods and at low water temperatures. In spring, newly hatched fry of S. alpinus may serve as an important host to maintain a G. salaris metapopulation within a river system. The results suggest that S. alpinus are adequate long-term hosts of G. salaris independent of the presence of the co-occurring highly susceptible S. salar .