ICHTHYOPHTHIRIUS MULTIFILIIS - OBSERVATIONS ON THE LIFE-CYCLE AND INDICATIONS OF A POSSIBLE SEXUAL PHASE

Theronts of the ciliate Ichthyophthirius multifiliis (Fouquet) with up to 4 micronuclei were recorded in populations from two different para site isolates, maintained as primary infections in juvenile carp throu gh 2 and 10 cycles, respectively. The largest number of multimicronucl eate forms occurred within the older isolate (10 cycles) following cys t incubation at 20 degrees C. Trophonts were induced to emerge from th e host epidermis following incubation of the fish in Eagles MEM for 10 -15 min at 20 degrees C. This provided for the first time a technique to recover trophonts in all stages of development; observations were m ade on the transition from theront to trophont, with respect to nuclea r events, the organelle of Lieberkuhn, 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 conjugat ion, anisogamy and senescence.