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.

Mode of attachment and histopathological effects of Macrogyrodactylus clarii, a monogenean gill parasite of the catfish Clarias gariepinus, with a report on host response

“…were not associated with any gross pathology. Similarly, Cusack (1986) reported that G. colemanensis did not influence the growth or survival of the fry of rainbow trout, Oncorhynchus mykiss and Cone and Cusack (1988) found no evidence of lesions in infections of G. colemanensis and G. salmonis on salmonids. Whether or not the histopathological effects produced by M. clarii influence the growth, survival and/or mortality of C. gariepinus still need to be studied experimentally.…”

Gyrodactylidae et Gyrodactylose des Salmonidae

“…This seems also to be valid to G. salmonis. In laboratory experiments (CONE et ODENSE, 1984;CUSACK, 1986;CUSACK et CONE, 1986;CONE et CUSACK, 1988), however, G. salmonis was pathogenic to the expérimental host, Salvelinus fontinalis, while infestations by G. co/emanens/s caused no clinical sign. This may imply that G. salmonis (G. sa/an's-group) is a true salmonid parasite, while G. colemanensis (G. arcuatus-group) is not spécifie to salmonids.…”

“…Hitherto, however, the species is not found on a spécifie host in natural waters. Furthermore, on salmonids in farms the species seems not to cause disease (CUSACK, 1986;CONE et CUSACK, 1988). Thus the species in fish farms may use salmonids as temporary hosts.…”

“…5) may be favourable to certain Gyrodactylus species and contribute to their spreading. Few spécimens of Gyrodactyluson individualsof stocked fish, wild fish entering the farm via the water supply (CONE et CUSACK, 1988), or even detached worms in the water intake may give rise to large populations of Gyrodactylus in a farm. The unnaturally large density of fish in the tanks will faveur the development of a Gyrodactylus population.…”

“…Furthermore,several expérimentalstudieson host-parasite relationships were performed (e.g. CONE et CUSACK, 1988;JANSEN, 1989;BAKKE et al, 1992b). From a biogeographic and epidemiological point of view, HALVORSEN et HARTVIGSEN (1989) made a critical examination of récent and earlier data on G. salaris.…”