Proliferative Kidney Disease in Feral Cutthroat Trout from a Remote Montana Reservoir: A First Case

Abstract Proliferative kidney disease (PKD) caused by the unclassified myxosporean referred to as PKX was found to be associated with mortality of feral cutthroat trout Oncorhynchus clarki in a remote Montana reservoir during August and September of 1990 and 1991. Affected fish had swollen and mottled kidneys, pale livers, and ascites. Microscopic examination of stained tissue sections revealed PKX in the gill, liver, and kidney. This report of PKD is the first in Montana and in feral cutthroat trout. This epizootic also raises questions regarding our knowledge of geographic distribution and potential impact of PKD on feral trout populations.