NON-SALMONID FISH INHABITING A HATCHERY WATER SUP- PLY ENZOOTIC FOR PROLIFERATIVE KIDNEY DISEASE IN- FECTED WITH ONE MYXOSPOREAN, Myxobilatus SP'P

Proliferative kidney disease (PKD), caused by an unclassified myxosporean (PKX), is a serious disease of salmonids. Although partial spore development occurs to a limited extent in fish infected with PKX, complete sporalation has not been observed and precise taxonomic status of PKX remains uncertain. The severe inflammation seen in infected fish, unusual for most myxosporean infections, suggest salmonid species are aberrant hosts for PKX. Recently, there has been considerable speculation that PKX belongs to the genus Sphaerospora (Feist, 1988; Hedrick et aI., 1986). Sphaerospores have been found in tui chub (Gila hieoIor) inhabiting the water supply of PKD-infected Hot Creek State Hatchery, California and stickleback (Gasterosteus aeuIeatus) from Quinalt Lake, Washington, which is the water supply of a PKDinfected steelhead hatchery (Hedrick et aI., 1988). Similar characteristics shared between PKX and Sphaerospora have been described by Kent and Hedrick (1986). Odening et aI. (1988) reported the simultaneous occurrence in rainbow trout of PKX and Sphaerospora spp., and unidentified myxosporean forms in swim bladder and intestinal walls. This report presents evidence that disputes the implicaton that PKD is caused by cross transmission of Sphaerospora spp. The first reported outbreak of PKD in North America was at the Hegerman, Idaho, State Fish Hatchery (SFH), rainbow trout (Onehorynehus mykiss)(Smith et aI., 1984). PKD was also diagnosed during an extensive examination of wild rainbow trout inhabiting Riley Creek, one hatchery water supply. At that time, intraluminal sporogonic forms similar to those report-