Submitted to: Journal of Fish Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/28/2002
Publication Date: 5/15/2002
Citation: Xu, D., Klesius, P.H. 2002. Antibody mediated immune response against Ichthyophthirius using excised skin from channel catfish, Ictalurus punctatus (Rafinesque), immune to Ichthyophthirius. Journal of Fish Diseases. 25, 299-306. Interpretive Summary: The ciliated protozoan Ichthyophthirius multifiliis, referred to as Ich, has a worldwide distribution and almost all freshwater fish are infected by this parasite. High fish mortalities and economic loss from Ich infection have been reported in both cultured and ornamental fish in the tens of million dollars annually. Although chemotherapy is commonly practiced, chemical treatments are either too costly for culture ponds or the chemica residues may cause human food safety concern. Uses of chemicals are also difficult to control the Ich infection since the parasite penetrates into fish skin and gills. Current chemical treatments require multiple applications of chemicals to the water to break the parasite's life cycle. No vaccine is available to prevent Ich disease currently. In this study, we collected fish skin from catfish immune to Ich and grew it in the culture medium. Then we treated infective Ich with culture fluids and determined if the Ich could retain the potential to infect fish. The results showed that the invasion was reduced greatly after the Ich was treated with immune culture fluids. Numbers of infected fish were lower in the treated group than untreated control. The antibody in the culture fluids prevented fish from Ich infection. The result indicates that use of vaccine could be developed.
Technical Abstract: This study investigated antibody mediated immune response against Ichthyophthirius multifiliis (Ich) by determining whether theronts could retain the potential for re-infection, both in vitro and in vivo, after treatment with the culture fluid of excised skin from channel catfish immune to Ich. Theronts were immobilized and agglutinated by the culture fluid from immune fish at the dilution 1:64 or lower. The invasion was reduced significantly (p< 0.05) for theronts treated with the immune culture fluid compared to theronts treated with the culture fluid of the excised skin from naive fish. At 4h post exposure (PE), more than 60% of control theronts treated with the culture fluid from naive fish penetrated into excised skin, but less than 30% of theronts treated with the immune culture fluid completed the invasion. The treatment of theronts with the immune culture fluid greatly reduced the size of trophonts compared to the tropont size developed from control theronts. The mean volumes of troponts developed from theronts treated with immune culture fluid were only 73.5% and 76.9% of control trophont volumes at 24 and 48 h PE. Trophonts developed from theronts treated with the immune culture fluid showed lower survival after 24h PE compared to those from control theronts. Eight out of 20 fish infected with theronts treated with immune culture fluid showed no trophonts on the skin. The remaining 60% of fish infected with the treated theronts had light infection with less than 50 troponts on the surface per fish. The infection was severe for fish invaded by theronts treated with the culture fluid from naive fish; the number of infected fish and the density of trophont per fish were high.