The microbial diversity of the intestinal tract content of the river trout from two Lithuanian rivers has been investigated by molecular methods: polymerase chain reaction amplification and sequencing of partial 16S rRNA genes. Predominant bacterial populations detected in the river trout intestinal tract from the Skorblus River were Rahnella (21%), from the Žeimena River, Aeromonas (41.7%) and Plesiomonas (22.9%). Buttiauxella agrestis, Budvicia aquatica, Erwinia persicinus, Yersinia mollaretii, Y. kristensenii, Y. rohdei, Moellerella wisconsensis, Obesumbacterium proteus, Pantoea cedenensis, Rahnella aquatillis, and Rahnella sp. from the Enterobacteriaceae family have been detected in the intestinal tract of freshwater salmonid fish for the first time.