Histopathology of furunculosis in brown trout Salmo trutta L.

. A histopathological description is given of 2 naturally‐occurring outbreaks of furunculosis in brown trout, one sub‐acute, the other chronic. The splenic ellipsoids were destroyed to a greater or lesser extent thereby leading to a collapse of vascular integrity of the organ. In chronically affected fish however, a proliferation of stromal cells including reticular sheath cells was additionally noted. Cardiac involvement was the most prominent feature of the chronically affected fish. The marked degree of destruction left little doubt that cardiac efficiency was very severely impaired.