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Title: Protective immunity of Nile tilapia against Ichthyophthirius multifiliis post immunization with live theronts and sonicated trophonts

Author
item Xu, Dehai
item Klesius, Phillip
item Shoemaker, Craig

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2008
Publication Date: 5/30/2008
Citation: Xu, D., Klesius, P.H., Shoemaker, C.A. 2008. Protective immunity of Nile tilapia against Ichthyophthirius multifiliis post immunization with live theronts and sonicated trophonts. Fish and Shellfish Immunology. 25: 124-127.

Interpretive Summary: Ichthyophthirius multifiliis (Ich) is a severe fish parasite that causes heavy mortality in many cultured fish, including Nile tilapia. The Ich infection is difficult to control with chemical treatments 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 tilapia against Ich even though tilapia suffer losses from this parasite like other fish. The objective of this study was to evaluate immune protection of tilapia against Ich after immunization with live or sonicated parasites by bath immersion and intraperitoneal (IP) injection. After the immunized fish were challenged with Ich 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 results of this study will be useful to fish farmers and the tilapia industry. The use of vaccines to prevent Ich disease can reduce fish loss and increase profitability.

Technical Abstract: Two immunization trials were conducted to evaluate host protection of Nile tilapia, Oreochromis niloticus against Ichthyophthirius multifiliis (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. The serum anti-Ich antibody and cumulative mortalities of tilapia were determined after theront challenge. 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. Host protection was acquired in fish immunized with live theronts by immersion or IP injection. Tilapia immunized with sonicated trophonts by IP injection were partially protected with a 57% - 77% survival in both trials. The immunized tilapia still acquired high survival 180 days post immunization even serum anti-Ich antibody titers were lower in the immune fish. The protection appears not to be solely depending on serum antibody response against Ich.