© 2022 The Authors.A strain, S-1T was isolated from rainbow trout (Oncorhynchus mykiss) exhibiting clinical symptoms of lens atrophy, inappe-tence, visual impairment and growth retardation. The strain was identified as representing a member of the genus Shewanella on the basis of the results of 16S rRNA gene sequence analysis. The neighbor-joining phylogenetic tree based on 16S rRNA gene sequences indicated that S-1T clustered with Shewanella putrefaciens JCM 20190T, Shewanella profunda DSM 15900T, and Shewanella hafniensis P010T, sharing 99.3, 98.8 and 87.7% 16S rRNA gene similarities, respectively. A polyphasic taxonomic approach including phenotypic, chemotaxonomic, and genomic characterization was employed to ascertain the taxonomic position of S-1T within the genus Shewanella. The overall genome relatedness indices (OGRI) for S-1T compared with the most closely related type strains S. hafniensis ATCC BAA-1207T, Shewanella baltica NCTC 10735T, S. putrefaciens ATCC 8071T and S. profunda DSM 15900T were calculated as 40.8, 40.1, 28.5 and 27.3% for digital DNA–DNA hybridization (dDDH), and 91.6, 91.0, 86.3 and 85.1% for average nucleotide identity (ANI), respectively. OGRI values between S-1T and its close neighbours confirmed that the strain represents a novel species in the genus Shewanella.The DNA G+C content of the strain is 45.2%. Major fatty acids were C17: 1 ω8c, C15: 0 iso, and summed feature 3 (C16: 1 ω6c and/or C16: 1 ω7c). The predominant polar lipids were phosphatidy-lethanolamine, phospholipid, amino-phospholipid and unidentified lipids. The major respiratory quinones were ubiquinone-8, ubiquinone-7 and menaquinone-7. Chemotaxonomic and phylogenomic analyses of this isolate confirmed that the strain represents a novel species for which the name Shewanella oncorhynchi sp. nov. is proposed, with S-1T as the type strain (JCM 34183T= KCTC 82249T).