Edwardsiella tarda is an enteric opportunistic pathogen that causes a great loss in aquaculture. This species has been described as a phenotypical homogeneous group; in contrast, serological studies and molecular typing revealed a wide heterogeneity. In this work, a proteomic study of differential expression of a virulent isolate from turbot cultured in the Norwest of Spain in comparison with an avirulent collection strain was performed in order to recognize proteins involved in virulence. One hundred and three proteins that presented different abundance were successfully identified and classified into 11 functional categories according to their biological processes: amino acid, carbohydrate and lipid metabolism, tricarboxylic cycle, stress response and protein fate, protein synthesis, biogenesis of cellular components, cell rescue defence and virulence, cell membrane and transport, signal transduction and purine and pyrimidine metabolism. Twenty three protein spots detected only in turbot isolate were identified. It was shown that the same proteins appeared in different spots in the two isolates. Mass spectra obtained by MALDITOF/TOF of some of these proteins and DNA sequencing explained the changes as a result of different amino acid sequences. Several proteins related with the virulence of E. tarda (FliC, ArnA or FeSODI) were only detected in the turbot European isolate. This article is part of a Special Issue entitled: HUPO 2014.