Identification of a cyprinid fish, the tench Tinca tinca L., as a carrier of the bacterium Aeromonas salmonicida, causative agent of furunculosis in salmonids.

A typical, pigment-producing strain of Aeromonas salmonicida (A. sal.), the causative agent of furunculosis in salmonid fish species, was isolated from a cyprinid species, the tench Tinca tinca L. with papilloma-like skin alterations. Histopathology of the papilloma-like skin alterations in tench revealed "round holes", distinctly lined by thick layers of epithelial cells, but no bacteria. The organism was isolated from skin, gills and fins, but not internal organs. The isolate proved highly virulent for both juvenile tench and brown trout Salmo trutta L. in experimental infection, but it did not reproduce the clinical picture. The causative role of A. sal. for the surface lesions remains questionable. However, there is a perceived risk of the organism's transmission between tench and other susceptible species of fish, especially farmed trout.