Aim To identify pathogen of diseased yellow perch and determine their virulence. Methods and Results Fifteen Gram-negative bacterial isolates were recovered from the skin lesions of diseased yellow perch (Perca flavescens). Based on API 20NE test, ten isolates were found to share 67 center dot 299 center dot 9% homologies with Chryseobactertium indologenes. Based on fatty acid methyl ester analysis, 13 isolates were found to share similarities with C.indologenes and other species of Chryseobacterium. Based on sequencing results of partial 16S rRNA gene, 13 isolates shared 99% identities (e value=2e50) with the 16S rRNA sequence of C.indologenes (GenBank HQ259684). Based on the 16S23S rRNA intergenic spacer region (ISR) sequence, the 13 isolates shared 88% identity (e value=1e165) with the 16S23S ISR sequence of C.indologenes (GenBank EU014570). T-coffee multiple sequence alignment revealed that the partial 16S rRNA or the 16S23S ISR sequence of the 13 isolates shared 100% identity with each other. When healthy yellow perch were exposed to the 15 isolates by bath immersion (c.6x107CFUml1 for 1h), only C.indologenes isolates killed 1020% of fish, whereas other isolates were avirulent. When yellow perch were exposed to C.indologenes by intraperitoneal injection, mortality was dose dependent, with LD50 and LD95 values of 1 center dot 5x108 and 3 center dot 2x108CFU per fish, respectively. Conclusions Chryseobactertium indologenes could be pathogenic to yellow perch. Significance and Impact of the Study This is the first report on the isolation of C.indologenes from diseased yellow perch. Virulence studies suggested that C.indologenes could become pathogenic to yellow perch.