Submitted to: Aquaculture Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 31, 2004
Publication Date: March 1, 2004
Citation: Xu, D., Klesius, P.H. 2004. Senescence of the parasite ichthyophthirius multifiliis by continual passage on channel catfish under laboratory conditions. Aquaculture Conference Proceedings. Technical Abstract: Ichthyophthiriasis, caused by ciliated protozoan Ichthyophthirius multifiliis Fouquet (Ich), is one of the serious parasitic diseases of fish and leads to heavy economic losses in aquaculture. Maintenance of the Ich culture in the laboratory is an important part of both applied and basic research. It is well recognized that repeated passage of Ich on fish leads to senescence of the parasite isolate. However, there is no study on the progress of parasite senescence. The objective of this study was to evaluate the progress of senescence of Ich after undergoing 104 serial passages on 2056 channel catfish for two years in the laboratory. This study demonstrated that the infection percentage was 90.7 ± 4.5 % (mean ± standard deviation) in early passage 1-25, which were significantly higher (p < 0.05) than those in other passages. Naive catfish were easily infected at the average ratio of 0.125 (1 infected fish : 8 naive fish) at Ich passage 1- 60. The parasites were progressively less infectious with the continuous passage. The higher ratio of infected to naive fish had to be used to maintain the parasite stock when using Ich from the older passages. The number of days for fish showing visible trophonts was significantly higher (7 days) when infected with Ich from older passages than from younger passages (5 days) at 22-24 °C.