© 2021 Elsevier GmbHDuring a study on culturable microorganisms from fish farms, four yellow-pigmented gram negative, rod shaped isolates, F-47T, F-339T, F-380 and F-400, were recovered from rainbow trout samples exhibiting clinical signs. Based on 16S rRNA gene sequence analysis, the strains were identified as members of the genus Flavobacterium. Strains F-47T and F-380 shared the highest 16S rRNA gene sequence identity level of 97.6% with the type strain of Flavobacterium frigoris DSM 15719T while strains F-339T and F-400 shared the highest identity level of 97.6% with the type strain of F. caseinilyticum AT-3-2T. A polyphasic taxonomic approach including phenotypic and genomic characterization as well as whole-cell MALDI-TOF mass spectrometry analyses was employed to ascertain the taxonomic position of the strains within the genus Flavobacterium. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses between strains F-47T, F-339T and their close neighbours F. frigoris DSM 15719T and F. caseinilyticum AT-3-2T, respectively, confirmed that both strains represent novel species in the genus Flavobacterium. The DNA G+C contents of the strains F-47T and F-339T are 34.3% and 35.3%, respectively. It can be concluded on the basis of polyphasic characterization as well as pairwise genome comparisons that the strains F-47T and F-339T represent two novel species within the genus Flavobacterium, for which Flavobacterium kayseriense sp. nov. F-47T (=JCM 34195T=KCTC 82255T) and Flavobacterium turcicum sp. nov. F-339T (=JCM 34202T=KCTC 82262T) are proposed, respectively.