Submitted to: Annual Meeting World Aquaculture Society
Publication Type: Proceedings
Publication Acceptance Date: December 10, 2008
Publication Date: February 15, 2009
Citation: Xu, D., Klesius, P.H., Shoemaker, C.A. 2009. Immunization of Catfish with Inactivated Trophonts Against Ichthyophthirius. In: Aquaculture America 2009, February 15-18,2009, Seattle, Washington. p. 381. Technical Abstract: The protozoan parasite Ichthyophthirius multifiliis (Ich) infests most species of fresh water fish worldwide and damages fish skin and gills. Epizootics have been reported in various freshwater fishes worldwide and result in severe economic loss to aquaculture. There are no chemical treatments effective in controlling Ich infection. Vaccination offers a preventive method against Ich. Various results have been reported in fish immunized with different Ich trophont preparations. The factors that influenced immunity following trophont immunization are not clear and need further study. Two trials were conducted to determine the effect of immunization with inactivated trophonts on serum and cutaneous antibody titers and survival in channel catfish. In trial I, catfish were intraperitoneally (IP) immunized with: 1) 1% formalin-inactivated trophonts, 2) 3% formalin-inactivated trophonts and 3) freeze-thawed trophonts. Positive and negative control catfish were immunized with live theronts and 5% bovine serum albumin (BSA), respectively. The formalin-inactivated or frozen trophonts were separately sonicated and adjusted to 2000 trophonts/ml in PBS for vaccination. Each fish was IP injected 10 µl/g fish of the antigen suspension corresponding to 20 trophonts/g fish. At day 14, 28 and 50 post immunizations, no statistical difference was noted in anti-Ich antibody titers in fish immunized with formalin-inactivated trophonts or freeze-thawed trophonts. The survival of immunized catfish ranged from 33.3% - 43.3% for the formalin-inactivated or freeze-thawed trophonts at 50 d post-immunization after challenge with theronts at a dose of 15,000 theronts per fish. The survival of the live theront and BSA-immunized catfish was 93.3 and 0%, respectively. In trial II, catfish were IP-immunized with sonicated trophonts at doses of 1) 5 trophonts/g fish, 2) 10 trophonts/g fish, 3) 20 trophonts/g fish and 4) 5% BSA as the control. Fish immunized with 10 or 20 trophonts/g fish showed highest serum (1/210- 1/480) and cutaneous antibody titers (1/48-1/52), respectively at 22 d post-immunization and survival (63.3 -60.0%). The fish immunized with 5 trophonts/g fish had titers of 1/52 and 1/12 for serum and cutaneous antibody and survival of 23.3%. BSA immunized catfish had background titers and a survival of 6.7%. There was a significant correlation between dose of sonicated trophonts used to immunize the fish and catfish survival (correlation coefficient=0.859, p<0.01). These results indicate that dose of sonicated trophonts is important in generation of acquired immunity to Ich.