Induction of proliferative kidney disease (PKD) in rainbow trout Oncorhynchus mykiss via the bryozoan Fredericella sultana infected with Tetracapsulabryosalmonae

Proliferative kidney disease (PKD) is a serious infection of wild and farme d salmonids, affecting mainly the kidney and spleen but becoming systemic i n most susceptible fish hosts. This report deals with the: transmission of Tetracapsula bryosalmonae Canning, Curry, Feist, Longshaw & Okamura 1999 fr om naturally infected bryozoans Fredericella sultana Blumenbach 1779 to nai ve rainbow trout Oncorhynchus mykiss Walbaum 1792, thereby confirming the r ecent conclusion based on partial 18S rDNA sequence data that bryozoans are hosts of the myxozoan parasite T. bryosalmonae (formerly PKX organism) tha t causes the disease. Parasite transmission using T. bryosalmonae spores wa s successful by short-term exposure to disrupted bryozoans known to contain T. bryosalmonae spores and T. bryosalmonae sacs liberated from the bryozoa ns, and by long-term cohabitation with infected bryozoan colonies. Infectio n was confirmed by examination of kidney imprints, detection of the parasit e in stained tissue sections, PCR using T. bryosalmonae-specific primers, a nd comparison of amplified 18S rDNA sequences from the bryozoans and experi mentally infected fish. Transmission was not apparent, nor was PKD induced, in fish challenged by intraperitoneal injection of spores isolated from E sultana.