A pathogenic strain X1 was isolated from Siberian Sturgeon (Acipenser baerii) suffering with bacterial septicaemia.The median lethal concentration (LC₅₀ ) of strain X1 was 5.62×10⁵ cfu/ml to healthy Siberian Sturgeon,which showed that strain X1 had rather strong virulence.Strain X1 was identified as Aeromonas hydrophila by physiological and biological studies and 16S rDNA sequence analysis,which indicates that it had close relativity with A.hydrophila strain ATCC35654 (locus number:X74676.1),with a high homology of 99%.Strain X1 was inactivated by 0.30% formalin and its whole cell vaccine was made to immune Siberian Sturgeon with injection.The experiment results showed that whole cell vaccine of A.hydrophila strain X1 could obviously enhance the level of serum anti-A.hydrophila antibodies-and the total counts of immunoglobulin,total proteins,as well as lysozyme.In addition,whole cell vaccine effectively prevented Siberian Sturgeon from being infected by A.hydrophila.The relative survival percent of Siberian Sturgeon was 50%.Further,whole cell vaccine with FIA improved relative survival percent to 70%,showing more effective immunity effect.Therefore,there is a potential to apply whole cell bacteria A.hydrophila strain X1 to prevention and cure of Siberian Sturgeon suffering with bacterial septicaemia.