Sporogony of Tetracapsuloides bryosalmonae in the brown trout Salmo trutta and the role of the tertiary cell during the vertebrate phase of myxozoan life cycles

摘要: Tetracapsuloides bryosalmonae is the myxozoan that causes commercially and ecologically important proliferative kidney disease of salmonid fish species. Immunohistochemistry electron microscopy were used to examine development this parasite within brown trout Salmo trutta. The main replicative phase T. a cell doublet composed primary single secondary cell. Engulfment one by another form secondary-tertiary (S-T doublet) heralded onset sporogony whereupon migrated tubule lumen. Within tubule, transformed into pseudoplasmodium anchored epithelial cells via pseudopodial extensions. each developed spore, 4 valve cells, 2 polar capsules 1 sporoplasm. pseudoplasmodia formed clusters suggesting large numbers spores develop fish. This examination suggests freshwater myxozoans vertebrates direct replication doublets rather than through rupturing extrasporogonic stages, while tertiary formation relates only sporogony. Taken in conjunction with existing phylogenetic data, 5 distinct sporogonial sequences are identified for Myxozoa.