Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2005
Publication Date: September 1, 2006
Citation: Xu, D., Klesius, P.H. 2006. Susceptibility of nile tilapia to infection of the parasite ichthyophthirius multifiliis. Journal of the World Aquaculture Society. Vol 37(3) p. 60-63. Interpretive Summary: A one-year study was conducted to evaluate the susceptibility of Nile tilapia to fish parasite Ichthyophthirius (Ich) infection. Nile tilapia is one of major farm raised fish but little information is available about the pathogenicity of Ich in this species. Ichthyophthirius causes high mortalities of fish and leads to heavy economic loss in aquaculture in the tens of million dollars annually. Tilapia were easily infected by exposing to live Ich infected fish, contacting with dead Ich infected fish or exposing to parasite theronts. More than 94% of tilapia became infected by any of these 3 methods and the fish showed 50-100 or more visible parasites per fish. These infection percentage and infection level in tilapia were similar to those in channel catfish. Exposure to Ich infected fish resulted in greater infection percentages and levels than exposure to theronts. Tilapia were more resistant to Ich infection and had a lower mortality than channel catfish. The results in this study provides new information on the susceptibility of tilapia to parasite Ich. The new information will be benefit the development of Ich vaccines.
Technical Abstract: Nile tilapia, Oreochromis niloticus L., is one of major farm raised fish but little information is available about the pathogenicity of Ichthyophthirius multifiliis Fouquet (Ich) in this species. This study evaluated the susceptibility of tilapia to Ich infection by cohabiting with live Ich infected fish, exposure to dead Ich infected fish and exposure to theronts. The parasite infectivity on tilapia was evaluated by determining the percentage of fish infected, the infection level and the infection ratio of Ich infected fish to naive fish used in the infection trials. Tilapia were easily infected by these methods when challenged with Ich from Ich passages or infection cycles 20-50. More than 94% of tilapia became infected by any of these 3 methods and the fish showed 50-100 or more visible trophonts per fish. Infection percentage and infection levels in tilapia were comparable to those in channel catfish. Tilapia were more resistant to Ich infection than channel catfish and fewer tilapia were killed by heavy Ich infection. Cohabitation with live Ich infected fish or exposure to dead Ich infected fish resulted in greater infection percentages and levels than exposure to theronts.