AQUATIC ANIMAL DIAGNOSTICS, PATHOGENESIS AND APPLIED EPIDEMIOLOGY
Location: Aquatic Animal Health Research
Title: A cohabitation challenge model in immunization trials for channel catfish against the parasite Ichthyophthirius
Submitted to: Annual Meeting World Aquaculture Society
Publication Type: Abstract Only
Publication Acceptance Date: November 6, 2007
Publication Date: February 10, 2008
Citation: Xu, D., Klesius, P.H., Shoemaker, C.A. 2008. A cohabitation challenge model in immunization trials for channel catfish against the parasite Ichthyophthirius. In: Aquaculture 2008. February 9-12, 2008. Orlando, FL. p.441.
Ichthyophthirius multifiliis (Ich) is a fish protozoan that causes severe economic losses in aquaculture. There are no chemical treatments truly effective in controlling Ich infection. However, vaccination offers a preventive method against Ich. A method which closely mimics natural exposure is needed for evaluation of protective immunity against Ich. This study evaluated a cohabitation challenge method in immunization trials against Ich using calcein, a fluorescent dye, to mark channel catfish.
To determine the effect of calcein on the susceptibility of fish to Ich theronts, fish were marked by calcein immersion at 0, 500 and 1500 mg L-1, respectively, and then challenged with 10,000 theronts per fish. No difference was noted on fish infection level, mortality and median day to death (MDD) between fish non-marked and marked with calcein or between marked with high (1500 mg L-1) and low (500 mg L-1) concentration of calcein.
After ensuring that calcein marking had no effect on the susceptibility of fish to Ich theronts, two immunization trials were conducted to evaluate the cohabitation challenge model using catfish marked with 500 mg L-1 calcein. Fish mortality, relative percent survival (RPS), and MDD were compared between cohabitation-challenged fish and fish challenged by non-cohabitation. No significant difference was observed in RPS for cohabitation-challenged fish and fish challenged by non-cohabitation. Cohabitation challenge is an alternative challenge method for parasite study since it closely mimics natural exposure, enables immunized and non-immunized fish to be compared within the same experimental unit and ensures that all the test fish are exposed to the same trial conditions, such as pathogen concentration, density of fish, and water quality.