Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2006
Publication Date: 3/13/2006
Citation: Xu, D., Klesius, P.H., Panangala, V.S. 2006. Induced cross protection in channel catfish, Ictalurus punctatus (Rafinesque), against different immobilization serotypes of Ichthyophthirius multifiliis. Journal of Fish Diseases, 29: 131-138. Interpretive Summary: Fish parasite Ichthyophthirius multifiliis (Ich) is highly infective for most species of fresh water fish worldwide and causes heavy economic loss in the aquaculture industry. Chemical treatment of Ich infection is difficult since the parasite penetrates into the fish skin and gills, the high cost involved in therapy, and the public’s concern for food and environmental safety. Immunizing fish with the parasite can provide protection against Ich infection from the same serotype. It is not clear if the fish immunized with Ich from different serotype could induce an immune response and provide cross protection against heterologous serotypes of Ich. In this study, we immunized channel catfish with two different serotypes of Ich, determined immune responses of fish and evaluated the cross protection against both homologous and heterologous serotypes of Ich. The results demonstrated that channel catfish immunized by either serotype of Ich developed an immune response against Ichthyophthirius, provided cross protection against challenge from both serotypes of the parasite. This study further demonstrated that vaccination of fish against Ich is an alternative to chemical treatments.
Technical Abstract: Channel catfish Ictalurus punctatus (Rafinesque) were immunized with Ichthyophthirius multifiliis (Ich) theronts and trophonts, and the immune response and host protection against both homologous and heterologous serotypes of Ich were evaluated. Immunizations were done with two serotypes (ARS4 & ARS6) of live theronts by bath immersion (Trial I) and with sonicated trophonts by intraperitoneal (IP) injection (Trial II). Cutaneous and serum antibody titers against Ich following immunization were measured, and survival of catfish was determined after theront challenge. Theronts were immobilized by the anti-serum from fish immunized with homologous theronts or trophonts, but not by the serum of fish immunized with the heterologous serotype. Serum from fish immunized by immersion with live theronts showed higher ELISA titers against both homologous and heterologous serotypes than fish by IP injection of trophonts. Channel catfish immunized by immersion with live theronts or by IP injection with sonicated trophonts developed an immune response against Ichthyophthirius and provided cross protection against challenge from both serotypes (ARS4 & ARS6) of the parasite. Sonicated trophont antigens in aqueous solution by IP injection could stimulate fish immune response, but last only a short period of time. Studies are needed for an adjuvant to improve vaccine efficacy and long-last immune protection.