Bacteria isolated from rainbow trout, Oncorhynchus mykiss, kept in a farm, in Turkey. During the outbreak, 40% of the rainbow trout (10-40 g) died. Typical clinical signs were exophthalmia, dark pigmentation, hemorrhage at the base of the pectoral, pelvic, anal fins and around the vent. Internal signs were enlarged spleen, pale liver and intestine filled with yellowish fluid. Liver, kidney and spleen of diseased fish, were aseptically streaked on Tryptic Soy Agar. After incubation, pure cultured colonies were observed and biochemically characterized with API 20 NE and other biochemical tests. Cultured bacterial 16 S rDNA gene was sequenced. Based on biochemical characteristics and sequence of 16 S rRNA, the causative bacteria were identified as Pseudomonas luteola. This study reports the first P. luteola infection in fish. (C) 2007 Elsevier B.V. All rights reserved.