Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2004
Publication Date: March 22, 2004
Citation: Xu, D., Klesius, P.H., Shelby, R.A. 2004. Immune responses of channel catfish against ichthyophthirius multifiliis after immunization with live theronts and sonicated trophonts. Annual Eastern Fish Health Workshop. Technical Abstract: The ciliated protozoan Ichthyophthirius multifiliis Fouquet (Ich) causes high mortality in fish and leads to heavy economic loss in aquaculture. The Ich infection is difficult to control with chemical treatments since the parasite penetrates into the fish skin and gills. Fish that survive an Ich infection acquire immunity against reinfection by the parasite and vaccination against the parasite can be used as an alternative to chemical treatments. This study determined the humoral immune responses and host protection of channel catfish Ictalurus punctatus (Rafinesque) against Ichthyophthirius multifiliis (Ich) after immunization with live theronts and sonicated trophonts, with an emphasis on assessing the cutaneous immune response. Immunizations with live theronts or sonicated trophonts were done by both bath immersion and intraperitoneal (IP) injection. Cutaneous and serum immunoglobulin (Ig) levels and anti-Ich antibodies were measured 12 and 21 days post immunization with the enzyme-linked immunosorbent assay and theront immobilization assay. The level of Ich infection and survival of catfish were determined after theront challenge at a dose of 15,000 theronts per fish for 1 hour. Cutaneous and serum anti-Ich antibodies were significantly higher in fish immunized with live theronts by immersion or IP injection or with sonicated trophonts administrated by IP injection compared to fish immunized with sonicated trophonts by immersion, with bovine serum albumin by IP injection, or non-immunized controls. Host protection was noted only in fish immunized with live theronts by immersion or IP injection or with sonicated trophonts by IP injection. There was a positive correlation between higher levels of anti-Ich antibodies and host survival in the immunized fish. Specific anti-Ich antibody levels appear to be a better indicator of Ich tolerance than total non-specific Ig.