Ichthyophthirius multifiliis: axenic isolation and short-term maintenance in selected monophasic media

Abstract. All stages in the life cycle of Ichthyophthirius multifiliis were successfully isolated axenically, without loss of viability, by use of 1% penicillin:streptomycin solution (100IUcm⁻³:100μg cm⁻³). Survival and development of each stage was investigated in selected monophasic media at 20°C. Parasite survival was extended over that observed in water controls, suggesting that both parasitic and free-living stages are capable of some degree of nutrient uptake. The tomite survived within the cyst for a maximum of 22 days when incubated in EMEM without added serum (EMEM-S) and diluted 50:50 with distilled water. Viable theronts survived for up to 5 days within EMEM, 3 days longer than controls, and mature trophonts survived, with no further development, for up to 16 days within Glasgow modification of EMEM with added 10% serum. Successful encystment and excystment was dependent on water and occurred only in diluted media. Delayed encystment was achieved by incubation in concentrated media, the production of sterile, viable theronts being delayed for up to 96h within EMEM-S, 72h later than normally observed in the aquatic environment. The significance of the results are discussed with regard to the routine maintenance of the parasite and future prospects for in vitro culture.