Little is known about the biology of this parasite and its life-cycle has only recently been resolved. Surprisingly, the Myxozoa have recently been shown to be highly reduced animals that are most closely related to cnidarians (jellyfish, hydras and corals) (Jiménez-Guri et al. 2007).
T. bryosalmonae develops into tiny, sac-like stages around 0.35mm in diameter in the body cavity of freshwater bryozoans. Each sac contains 1000’s of infectious stages (spores). Parasite stages in fish consist of only several cells.
Laboratory studies indicate that sac-like stages can develop within 3 days from single cell stages in bryozoan hosts (Canning & Okamura, 2004). Transmission studies demonstrate that it takes some 3-8 weeks from the time of infection for stages to develop in fish kidney, depending on temperature (Gay et al. 2001).
Long term infections of bryozoans appear to be maintained by:
When fish survive infection the parasite may persist for at least one year (Foott and Hedrick, 1987), and perhaps for the lifetime of the fish. Spores are infective for <24 hr (De Kinkelin et al. 2002 ).