Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 13, 2005
Publication Date: February 13, 2006
Citation: Xu, D., Klesius, P.H., Panangala, V.S. 2006. Ichthyophthirius (Ich) induced cross protection in channel catfish against different serotypes of Ich. Aquaculture America Conference. Technical Abstract: Ichthyophthirius multifiliis is one of fish parasites that infects most species of fresh water fish and causes heavy economic loss in the aquaculture industry. This study was designed to immunize channel catfish with Ich theronts and trophonts, determine serum and cutaneous immune responses of fish and evaluate the cross protection against both homologous and heterologous serotypes of Ich. Immunizations were done with two serotypes (ARS4 & ARS6) of live theronts by bath immersion and with sonicated trophonts by intraperitoneal (IP) injection. Twelve tanks with 28 catfish per tank were divided equally into 3 groups. Each group of fish was immunized by exposure to ARS4 or ARS6 or theront free water (control), respectively. Fish were exposed to live theronts at a dosage of 5000 theronts per fish for one hour. For immunization with trophonts, fish in 12 tanks were divided into 3 groups and immunized by IP injection with: 1) sonicated ARS4 trophonts at a dosage of 20 trophonts/g of fish, 2) sonicated ARS6 trophonts at a dosage of 20 trophonts/g of fish, and 3) 5% bovine serum albumin. Two to four fish from each tank were removed and serum and cutaneous antibody measured at 12 and 22 days after immunization. Antibodies against Ich in skin culture fluid and serum were determined with the theront immobilization assay and antibody titers determined by enzyme-linked immunosorbent assay (ELISA). Each immunizated group of fish was divided into two sub-groups and challenged with either ARS4 theronts or with ARS6 theronts at a dose of 15,000 theronts per fish for 1 h. The clinical signs and mortality of fish were monitored daily for 3 weeks. Theronts were immobilized by the anti-serum from fish immunized with homologous theronts or trophonts, but not by the serum from fish immunized with heterologous serotype. Serum from fish immunized by immersion with live theronts or by IP injection of trophonts showed higher ELISA titers against both homologous and heterologous theronts compared to serum from the control fish. The antiserum from immunized fish failed to immobilize heterologous theronts, however, antiserum reacted with heterologous theront proteins that were used in the ELISA assay, given OD readings higher than serum from non-immunized controls. Channel catfish immunized by immersion with live theronts developed an immune response against Ichthyophthirius and provided cross protection against challenge with both serotypes (ARS4 & ARS6) of parasite. Among fish immunized with sonicated trophonts by IP injection, and challenged with homologous and heterologous theronts, survival rates were 95% and 75%, respectively. Most of the non-immunized fish died after challenge exposure to theronts.