We selected the European eel (Anguilla anguilla )the body weight was 70 to 100g, tostudy the expression of the cecropin cDNA, which was driven by a humancytomegalovirus (pCMV-cec) promoter, introduced into the eel by the in vivo injectionat liver or taking orally, The challenge by (Pseudomonas spp ) will be conducted andthen the effects of rearing in the closed recirculating system will be studied.