Manifestation of Proliferative Kidney Disease in Chinook Salmon (Oncorhynchus tshawytscha) Following Transfer of Infected Smolts to Sea Water

Abstract

For 4 consecutive years, the prevalence and severity of proliferative kidney disease (PKD), caused by the PKX myxosporean, in chinook salmon (Oncorhynchus tshawytscha) from the Puntledge River Hatchery, Vancouver Island, British Columbia, Canada was investigated after the fish were transferred to sea water. In the spring of 1991 through 1994, smolts were transferred from the hatchery to the Pacific Biological Station (PBS), Nanaimo, British Columbia at about the same time that their cohorts were released for seaward migration. In 1991, fish were maintained in PKX-free fresh water, and in 1992 fish were maintained in a seawater neetpen. In 1993 and 1994 fish were maintained in seawater tanks maintained at 15-17°C. In all years, virtually all the fish were subclinically infected with PKX at the time of transfer from the hatchery, and a prevalence of almost 100% was eventually observed in the fish after they were transferred to PBS. This study demonstrates that PKD can occur in sea water in post smolts originating from watersheds where the PKX parasite is present. It is, therefore, possible that PKD may impact ocean survival of salmon originating from PKX enzootic watershed, particularly because the disease causes osmoregulatory imbalances and anemia.