Submitted to: World Aquaculture Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2009
Publication Date: 3/1/2010
Citation: Xu, D., Klesius, P.H., Shoemaker, C.A. 2010. Protective immunity of Nile tilapia against Ichthyophthirius [abstract]. World Aquaculture Society. p. 1111.
Technical Abstract: Tilapia are currently cultured in different types of production systems ranging from pond, tank, cage, flowing water and intensive water reuse culture systems. Intensification of tilapia culture requires methods to prevent and control diseases to minimize the loss. Ichthyophthirius multifiliis (Ich) is one of the most virulent ciliated parasites of freshwater fish and causes serious problems in intensively cultured fish. The Ich infection is difficult to control using chemotherapy since the parasite penetrates into the fish skin and gills. Acquired immunity is an alternative way to prevent fish death against this parasite. Very little is known about the immune response of Nile tilapia against Ich even though tilapia are infested by this parasite like other fish. The objective of this study is to evaluate immune protection of Nile tilapia against Ich after immunization with live theronts or sonicated trophonts. Two immunization trials were conducted to evaluate host protection of Nile tilapia against Ich. Immunizations were done with live theronts or sonicated trophonts by bath immersion and intraperitoneal (IP) injection. The immunized fish were challenged with theronts 21 days post immunization in trial I and 180 days post immunization in trial II. Twelve tanks with 20 tilapia (10.5 cm in length and 17.6 g in weight) per tank were assigned for trial I. These fish were divided into 6 replicated groups and immunized as follows: 1) with live theronts by immersion at the dose of 20,000 theronts per fish; 2) with live theronts by IP injection at the dose of 20,000 theronts per fish; 3) with sonicated trophonts by IP injection at dose of 20 trophonts/g of fish; 4) with sonicated trophonts by immersion at 100 trophonts/g of fish; 5) with 5% bovine serum albumin in PBS by IP injection; and 6) non-immunized control. The serum anti-Ich antibody titers and cumulative mortalities of tilapia were determined after theront challenge at a dose of 40,000 theronts per fish. Trial II consisted of 12 tanks with 25 tilapia per tank. The procedure for immunization was the same as trial I except fish were challenged with 80,000 theronts per fish. Serum anti-Ich antibody was significantly higher (p<0.05) in tilapia immunized with live theronts by immersion or IP injection or with sonicated trophonts administered by IP injection than tilapia immunized with sonicated trophonts by immersion, with bovine serum albumin by IP injection, or non-immunized controls. After the immunized fish were challenged with Ich theronts 21 days post immunization in trial I and 180 days post immunization in trial II, high survivals (87-100%) were acquired in fish immunized with live parasite by immersion or IP injection. Tilapia immunized with sonicated parasites by IP injection were partially protected with a 57% - 77% survival in both trials. The immunization not only provided short term protection but also long term immunization of tilapia against Ich re-infection. The use of vaccines to prevent Ich disease can reduce fish loss and increase profitability for the aquaculture industry.