Abstract: To evaluate the mechanism of different spoilage potential of the specific spoilage organism(SSO), Shewanella, H₂S-producing bacteria isolated from the refrigerated Larimichthys crocea were identified using the physicochemical reactions and 16S rDNA.Four strains with different spoilage potential were selected in the sterile fish juice and fish block.The gene and expression of trimethylamine oxidation(TMAO)reductase in four strains were amplified and determined, and physicochemical properties of the protein were predicted.The results showed that all H₂S-producing bacteria were identified as Shewanella, in which S.baltica, S.putrefaciens and S.hafniensis accounted for 54.5%, 40.9% and 4.5%, respectively.Significant differences of the spoilage potential were in fish juice among Shewanella observed.The sensory score and TVB-N content of isolates S.baltica XH2 and XH8 were significantly higher than those of the other strains(P<0.05), whereas the indicators of isolates S.putrefaciens XH14 and XH17 were the lowest.The sample inoculated S.baltica XH2 was found to produce off-odors after 72 h, higher than 10⁷ cfu/g of TVC after 48 h, strong reduction ability of TMAO to TMA, high accumulation of TVB-N, cadaverine and putrescin, followed by S.baltica XH8, S.putrefaciens XH14 and XH17.The 2 490 bp fragment of torA gene were amplified in four Shewanella isolates.Expression of torA gene of four isolates was correlated with the spoilage potential.Furthermore, the highest molecular weight and aliphatic index of predicted TorA protein were observed, whereas theoretical pI and gravy were the lowest in S.baltica XH2.Thus, SSO in chilled L.crocea was S.baltica XH2, and the high spoilage potential in the isolate was associated with high level of torA expression and some physicochemical properties of TorA protein.It provides a good foundation to clarify the mechanism of spoilage in Shewanella.