Development of the PKX myxosporean in rainbow trout Salmo gairdneri

Abstract

Sequential development of PKX, the causative agent of prohferahve hdney dlsease, isdescnbed in rainbow trout Salmo ga~rdnen hchardson by light and electron mlcroscopy Fish wereexposed to water contaming the infechous stage of PKX and the parasite was detected 3 wk laterParasites were prominent the following week and they mulhplied by endogeny, binary fission andpossibly plasmotomy in the blood and hdney intershhum Intershbal nephnbs that is typicallyassoclated th PKD was fust observed 5 wk after exposure and was most prominent between 8 to11 wk At 7 wk parasites were found in the lumens of the tubules, many were daughter cells releasedfrom PKX Myxosporean sporoblasts formed within these daughter cells (enveloping cells) Thesporoblasts consisted of 6 cells and some organized into spores w~th 2 spherical polar capsulesAlthough the spores persisted for several months after the interstitial PKX and assoclated inflammationhad subsided they dld not complete their development They remained within the enveloping cell andapparently dld not form complete valves Because only incomplete spores were observed salmonidsmay be abnormal hosts and the preclse taxonomic status of PKX was not determined Epizoohologicaland sequential development data support the hypothesis that the interstitial form of PKX and theintraluminal myxosporeans belong to the same organism