Natural and Laboratory Transmission of the Marine Myxozoan Parasite Kudoa thyrsites to Atlantic Salmon

Abstract

Experiments were conducted to evaluate routes of transmission and subsequent development of Kudoa thyrsites (Myxozoa: Myxosporea) in Atlantic salmon Salmo salar. Atlantic salmon that were held for a 2-week exposure period at the seawater net-pen site and then transferred to freshwater tanks developed K. thyrsites infections as evidenced by the presence of myxospores in the somatic musculature at 3 months postexposure. Attempts to transmit the parasite directly from fish to fish by intubation of fresh myxospores were unsuccessful. However, the parasite was transmitted to Atlantic salmon by intraperitoneal injection of blood collected from a coho salmon Oncorhynchus kisutch infected with K. thyrsites. The waterborne infective stage of K. thyrsites was not removed by filtration of seawater entering the tanks at the Pacific Biological Station.