Theronts of the ciliate Ichthyophthirius multifiliis (Fouquet) with up to 4 micronuclei were recorded in populations from two different parasite isolates, maintained as primary infections in juvenile carp through 2 and 10 cycles, respectively. The largest number of multimicronucleate forms occurred within the older isolate (10 cycles) following cyst incubation at 20"C. Tro-phonts were induced to emerge from the host epidermis following incubation of the fish in Eagles MEM for 10-15 min at 20"C. This provided for the first time a technique to recover trophonts in all stages of development; observations were made on the transition from theront to trophont, with respect to nuclear events, the organelle of Lieberklihn, and phagocytosis of host cells. On re-exposure of carp already carrying a two-day primary infection, recently entered trophonts were found in various stages of fusion with established parasites. Results are discussed with respect to conjugation, anisogamy and senescence.
Ichthyophthirius multifiliis Fouquet, 1876, a ciliate parasite, is a cosmopolitan and problematic parasite of cultured freshwater fish. Each geographical isolate of I. multifiliis has variations in life cycle timing under different abiotic water conditions, such as temperature and salinity. We assessed the effects of salinity and temperature on the development and the preferred settlement site of a temperate Australian isolate of I. multifiliis. The time until theront release was significantly different between each temperature; development time was longest at 5 °C with a mean time of 189 h and decreased to a mean time of 11.7 h at 30 °C. At 5 °C our isolate produced a mean of 267 theronts per tomont, which increased to a mean of 493 theronts at 25 °C and reduced to a mean of 288 theronts at 30 °C. Theront length showed an inverse relationship to temperature; mean length was 62 μm at 5 °C and 41 μm at 30 °C. Our isolate reproduced faster at all temperatures and a greater sensitivity to salinity than all reported profiles for temperate isolates. Parasite abundance was highest on the dorsal region of the fish. An accurate understanding of temperature-life cycle information and optimal region to sample for surveillance will aid in the development of specific management plans for the Australian isolate of I. multifiliis, facilitating the strategic timing of treatments., James M. Forwood, James O. Harris, Matt Landos, Marty R. Deveney., and Obsahuje bibliografii