A study of Gyrodactylus colemanensis Mizelle and Kritsky, 1967 and Gyrodactylus salmonis (Yin and Sproston, 1948) (Monogenea) parasitizing captive salmonids in Nova Scotia

Abstract

Gyrodactylus colemanensis Mizelle and Kritsky, 1967 and Gyrodactylus salmonis (Yin and Sproston, 1948) parasitized Salvelinus fontinalis, Salmo gairdneri, and Salmo salar at a fish farm in Nova Scotia. Gyrodactylus colemanensis occurs on the edges of fins and clings delicately to the skin surface. Gyrodactylus salmonis embeds its marginal hooks deeply into the epidermis and occurs all over the body surface except on the fin edges. The parasites gain entrance to the hatchery on infected stocks arriving from other facilities and possibly through infected wild salmonids entering via the water supply. Brood stocks serve as reservoir hosts within the farm. Young-of-the-year S. fontinalis became infected within 8 weeks of transfer to the outside raceways, with hatchery buckets and nets likely serving as vehicles of transmission. Intensity of infection increased during winter to a spring peak followed by a decrease during the summer months. Intensity generally decreased with host age. Stocks were initially infected with mixed infections; subsequently, single species infections occurred which involved first G. salmonis, then G. colemanensis, and then G. salmonis. There were no clinical signs of disease associated with infections and the parasites did not harbor bacterial or viral pathogens.