Abstract: In order to determine the pathogen of the Carapace ulcer of Litopenaeus vannamei in factory freshwater aquaculture and provide the methods of prevention and treatment, analysis of isolation and identification of pathogens, virulence genes, toxicity test, the influence of phase related antibiotics and topical disinfectants on the aquatic animal were couducted. Samples were collected and isolated from the hepatopancreas of diseased shrimps and attacked water, and cultured with TCBS medium, screening for dominant strains of each group, respectively called F-L and F-W. Each group was identified based on the culture characteristics and forms, sequences of 16S rRNA gene and biochemical identification. The result of the F-L was Aeromonas veronii, and of the F-W was Aeromonas punctata. In virulence genes test, F-L strains detected 8 genes, respectively were aerA, Act, Lip, Fla, Exu, Ser, Alt and ahyB, and F-W strains had aerA, Alt, Lip, Fla, ahyB and hlyA. In toxicity test, both strains of bacteria could cause the death of Litopenaeus vannamei, and median lethal dose was 107.68 and 107.8 cfu/mL, respectively. The study would provide a basis of the effective prevention and control of Carapace ulcer of Litopenaeus vannamei caused by Aeromonas.

Key words: Aeromonas, Litopenaeus vannamei, freshwater aquaculture, factory aquaculture, antimicrobial susceptibility test