Lifecycle
Spores showing 4 polar capsules (spores approx. 18µm in diameter)
The parasite develops first as single cells associated with the bryozoan body wall, causing covert infections (Tops et al. 2006; Morris et al. 2006). The subsequent development of spore-forming sac-like stages (Canning et al. 2000) in the body cavity causes overt infections.
Spores released from bryozoans into the water attach to fish via a filament that everts from intracelular organelles (polar capsules) within spores. Attachment to skin or gills allows invasion of fish hosts by amoeboid cells that then proliferate in blood prior to reaching the kidney.
The formation and replication of cell doublets occurs in kidney tissue prior to spore production (Morris and Adams, 2008). Spores released in urine of brown and brook trout have been demonstrated to infect bryozoans (Morris and Adams, 2006; Grabner and El-Matbouli, 2008). No fish to fish or bryozoan to bryozoan transmission has been shown.