• Proceedings of the Korean Society of Fisheries Technology Conference
• /
• 1997.06a
• /
• pp.279-281
• /
• 1997

• Journal of fish pathology
• /
• v.10 no.2
• /
• pp.113-123
• /
• 1997

Concerned to the life cycle of Ichthyophthirius multifiliis, the biological characteristic of the parasites was studied in the rainbow trout (Oncorhynchus mykiss) and the Korean catfish (Silurus asotus) Under the experimental condition of $9^{\circ}C$- $28^{\circ}C$, tomitogenesis rate was positively proportional to water temperature, but not at over $28^{\circ}C$. The protomonts showed a high rate of tomitogenesis at $26^{\circ}C$ in comparision with other temperature conditions. Temperature affected tomitogenesis rate which resulted from the various conditions of salinity, pH and formalin concentration. The protomonts showed a high rate of tomitogenesis at pH 6.9 in comparision with other pH conditions at all temperatures tested. This result revealed that the opitimum pH for tomitogenesis was 6.9. The protomont had more tolerance against salinity and formalin concentration at low temperature ($18^{\circ}C$) than at high one ($22^{\circ}C$). Both trophont and protomont were not infective, but theront was infective.

• Journal of fish pathology
• /
• v.11 no.1
• /
• pp.51-60
• /
• 1998

Concerned to the lyfe cycle of Ichthyophthirius multifiliis, the experimental infection and development of the parasites were studied in the several freshwater cultured fishes. Opitimum conditions for the propagation of the parasite by serial passage with the rainbow trout fry was observed. Visiable white spots were examined in the body surface, fins and gills of the healthy fries, and a stable infection has been maintained for 2 months in the experimental system (Temperature: $18{\pm}1^{\circ}C$ DO: 7-7.5 ppm; pH: $7{\pm}0.2$). Induction conditions for artificial infection of the parasite by interms of the host fishes, stages of the parasites, and rearing temperature regimes was investigated. Rainbow trout fries showed a positive infection which was resulted from exposure of theront at $18^{\circ}C$. The rainbow trout fries induced white spots on the body surface at 3-7 days exposure to the theronts at $18^{\circ}C$. It was found that exposure of the rainbow trout fries exposed to 1,000 theronts per fish (10 theront/ml) for 45-60 minutes at $18^{\circ}C$ would consistently produce infection. Perfect infection (100%) was induced when the fries were exposed to 1,500 theront per fish (15 theront/ml) under laboratory condition. Development of I. multifiliis in the rainbow trout was observed for 7 days postexposure (PE). The parasite increased in average diameter from $54{\mu}m$ on the 1st day PE to $426{\mu}m$ on the 7th day PE. In the initial infestation period, the parasites were found on the gill epithelium, and on the 3rd day PE they invaded into the basal part of the gill filament adjacent to the major blood vessels, particularly the afferent vessels. Morphological change of buccal apparatus were observed on the 2nd day PE. Contractile vacuoles were more prominent on the 4th day PE, and they had notable changes on the 7th day PE.