Development of the PKX myxosporean in rainbow trout Salmo gairdneri

Abstract

Sequenhal development of PKX, the causative agent of prohferahve h d n e y dlsease, is descnbed in rainbow trout Salmo ga~rdnen hchardson by light and electron mlcroscopy Fish were exposed to water contaming the infechous stage of PKX and the parasite was detected 3 wk later Parasites were prominent the following week and they mulhplied by endogeny, binary fission and possibly plasmotomy in the blood and h d n e y intershhum Intershbal nephnbs that is typically assoclated \nth PKD was fust observed 5 wk after exposure and was most prominent between 8 to 11 wk At 7 wk parasites were found in the lumens of the tubules, many were daughter cells released from PKX Myxosporean sporoblasts formed within these daughter cells (enveloping cells) The sporoblasts consisted of 6 cells and some organized into spores w ~t h 2 spherical polar capsules Although the spores persisted for several months after the interstitial PKX and assoclated inflammation had subsided they dld not complete their development They remained within the enveloping cell and apparently dld not form complete valves Because only incomplete spores were observed salmonids may be abnormal hosts and the preclse taxonomic status of PKX was not determined Epizoohological and sequential development data support the hypothesis that the interstitial form of PKX and the intraluminal myxosporeans belong to the same organism V exposed to PKX at the American h v e r hatchery