A Gram-stain-negative, anaerobic and rod-shaped bacterium was isolated from gut of rainbow trout in Japan. The temperature range for the growth of 9N8T was 10–30 °C with an optimum at 20 °C. The organism produced acetate and butyrate when grown on AccuDia™ Gifu Anaerobic Medium broth, Modified. Phylogenetic analysis of 16S rRNA gene sequences indicated that strain 9N8T was related to the genus Fusobacterium (<92.9% similarity) and formed a distinct phylogenetic lineage from existing genera within the family Fusobacteriaceae. Strain 9N8T has a genome size of 2.60 Mb. The genomic DNA G+C content was 29.4 mol%. Average amino acid identity values between strain 9N8T and strains in the family Fusobacteriaceae ranged from 39.2 to 57.5%. The major fatty acids of strain 9N8T were C14 : 0, C16 : 1 ω7c and C16 : 0. On the basis of the morphological, physiological, biochemical and genetic information, a novel genus and species, Piscibacter tructae, is proposed, with 9N8T (=NBRC 116745T=DSM 118263T) as the type strain.