By Peder A. Jansen, Tor A. Bakke
Fisheries Research, Volume 17, Issues 1-2, Pathological Conditions of Wild Salmonids, June 1993, Pages 103-114, ISSN 0165-7836, DOI: 10.1016/0165-7836(93)90010-5.

The development of infrapopulations of Gyrodactylus salaris on wild Atlantic salmon parr (Salmo salar) from the River Lierelva was followed under experimental conditions, to assess the impact of various processes on this host-parasite system. Two experiments were performed. (1) The development of infrapopulations was followed from January to May 1991 on 24 naturally infected 1 + and older salmon parr. The fish were held individually isolated in two larger tanks in a fish farm in constantly flowing water supplied directly from the tributary River Glitra. (2) The development of infra-populations was followed in five consecutive groups, covering approximately 1 year, of about 20 1 + and older naturally infected and individually marked salmon parr. The fish were held in two parallel cages submerged in a channel connected to the River Lierelva.
In both experiments the infrapopulations of Gyrodactylus salaris increased markedly on all salmon parr with the spring rise in water temperature. Mortality of individual fish in this period was significantly and positively related to intensity of infection. In summer and autumn both increasing and decreasing infrapopulations were observed in all groups, revealing an increasing heterogeneity in resistance among the salmon parr, and consequently a negative impact of host resistance on the parasite population as the summer proceeded. Winter temperatures affect the population growth of the parasite negatively.

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