TRANSMISSION OF PKX, THE CAUSATIVE AGENT OF PROLIFERATIVE KIDNEY-DISEASE (PKD), TO RAINBOW-TROUT ONCORHYNCHUS-MYKISS FOLLOWING FILTRATION OF WATER AND SEDIMENTS

PKX, the myxosporean causing proliferative kidney disease (PKD), was transmitted to rainbow trout Oncorhynchus mykiss following their exposure to filtered sediments and water from a recycled water system where PKD is enzootic. Suspended sediments (25 1) were passed sequentially through 500, 250, 100 and 50 mum screens. Infectivity was found with material trapped at 500 mum and in water passing the 50 mum screen. No infectivity was found with material trapped on the 250, 100 or 50 mum screens. In a second study, 180 l of water was passed sequentially through a series of filters identical to those used in the sediment trial. No infectivity was trapped on any size filter (500 to 50 mum) but 10 of 20 trout exposed to water passing all filters were infected with PKX. The association of PKX infectivity with material >500 mum in the sediments and with a stage smaller than 50 gm in the water is consistent with the hypothesis that a second host residing in the sediments releases a smaller infective stage found in the water, as shown for other myxosporean/actinosporean parasite life cycles. A small oligochaete (Stylaria lacustris) found on the 500 mum filter is under investigation as the possible second/alternate host of the PKX myxosporean.