Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2004
Publication Date: 3/1/2004
Citation: Xu, D., Klesius, P.H. 2004. Two year study on the infectivity of Ichthyophthirius multifiliis in channel catfish Ictalurus punctatus. Diseases of Aquatic Organisms. 59:131-134. Interpretive Summary: Ichthyophthirius multifiliis (Ich) is one of serious fish parasites and causes heavy economic loss for aquaculture in the tens of million dollars annually. Ich is an obligate parasite and requires fish to propagate. There is no information available on long-term Ich senescence. This study evaluated the progress of senescence of Ich after undergoing 105 serial passages in channel catfish over a two year period. The infection level was higher in fish infected with Ich from serial passage 1-25 than with Ich from 26-105 passages. Catfish were infected at the ratio of 1 infected fish to 8 non-infected fish when using Ich from serial passages 1- 60, but the higher ratio had to be used to infect fish when using Ich from serial passages 61-105. The average time to show trophonts on fish was longer (7 days) using Ich from serial passages 91-105 than using Ich from serial passages 1-25 (5 days) at 22-24 °C. The result demonstrated the progress of long-term Ich senescence and provided an in vivo method for maintenance of Ich culture. This is the first verification of Ich senescence. The information is benefit to both applied and basic research on Ich, especially studies required long term maintenance of Ich culture.
Technical Abstract: Ichthyophthirius multifiliis Fouquet (Ich) is one of serious fish parasites and causes heavy economic loss for aquaculture. A serious difficulty in the maintenance of any single isolate of Ich for research is senescence. After an unknown number of serial passages the Ich isolate becomes senescent in its infectivity. The objective of this study was to determine the progress of Ich senescence during 105 serial passages in channel catfish (Ictalurus punctatus) over a two year period. The mean percentage of Ich infected fish, the infectivity levels and the time to trophont emergence were determined at 4 serial passages of 1-25, 26-60, 61-90, and 91-105 periods. Results of this study demonstrated that Ich was significantly more infective (p < 0.05) at serial passage 1-25 period than from 26-105 periods. Channel catfish were infected at the co-mingle infection ratio of 1 infected fish to 8 naive fish at serial passage 1-25 and 26- 60 periods. A higher co-mingle infection ratio was needed at serial passage 61-90 and 91-105 periods. The trophont emergence was noted to be significantly longer at serial passage 91-105 period compared to the serial passage 1-25 period, 7 to 5 days respectively at 23.4 ± 1.1 °C. The results of the present study indicated that senescence of I. multifiliis began after 25 serial passages and was predominate in the single Ich isolate at serial passage 61-90 and 91-105 periods.