Life Cycle Summary
The adult parasite (the trophont) is endoparasitic within the host fish and may undergo division whilst in the host. Each trophont appears as a small white spot on the skin of the infected fish. The duration of this stage is temperature-dependent and may last about 7 days at 20˚C. In temperate regions, the parasite can overwinter within the host for an increased duration of 3-4 months recorded at 3˚C. The exit from the host into the aquatic environment is an active process possibly involving the discharge of contractile vacuoles. In the aquatic environment the trophont encysts and the resultant tomont undergoes repeated binary fission, producing a population of approximately 50-3000 tomites. The tomites then differentiate into theronts, the infective stage of the life cycle. Tomonts can survive temperatures ranging from 2 to 27˚C and division times vary with temperature from 6 days to 10 hours as temperature increases. Theronts can survive around 22.5 hours at 20˚C although viability drastically declines after 12 hours. There are no recorded findings of sexual reproduction in I. multifillis although this seems unusual for ciliates and there are possible opportunities for conjugation within the life cycle. ref.
The adult parasite (the trophont) is endoparasitic within the host fish and may undergo division whilst in the host. Each trophont appears as a small white spot on the skin of the infected fish. The duration of this stage is temperature-dependent and may last about 7 days at 20˚C. In temperate regions, the parasite can overwinter within the host for an increased duration of 3-4 months recorded at 3˚C. The exit from the host into the aquatic environment is an active process possibly involving the discharge of contractile vacuoles. In the aquatic environment the trophont encysts and the resultant tomont undergoes repeated binary fission, producing a population of approximately 50-3000 tomites. The tomites then differentiate into theronts, the infective stage of the life cycle. Tomonts can survive temperatures ranging from 2 to 27˚C and division times vary with temperature from 6 days to 10 hours as temperature increases. Theronts can survive around 22.5 hours at 20˚C although viability drastically declines after 12 hours. There are no recorded findings of sexual reproduction in I. multifillis although this seems unusual for ciliates and there are possible opportunities for conjugation within the life cycle. ref.
