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Manipulative positioning of Gyrodactylus colemanensis on individually isolated fry of Salmo gairdneri was used to examine the behavior of the parasite during colonization and the influence that site of invasion has on size and spatial distribution of ensuing infrapopulations. The parasite's initial response was to relocate posteriorly on the host's body; those that reached a fin usually end up on or adjacent to the fin's margin. Individuals monitored for up to 15 days postinfection moved both anteriorly and posteriorly on the body surface and relocated to new fins via the body surface. The parasite occurred most frequently on the caudal fin followed by the pectoral and pelvic fins, with length of the fin margin and fin activity appearing to be factors influencing the distribution. Infections originating from the head, flank, and caudal fin similarly rose and fell to extinction or near extinction on the host over 49 days at 10 C. The more posterior the site of invasion, the greater the proportion of parasites carried by the caudal fin. The study concludes that G. colemanensis is restricted in its distribution on the host and that the fin margins may serve as a reliable food source and favor transmission to new hosts. |
