YELLOW PIGMENTED FILAMENTOUS BACTERIA CONNECTED WITH FARMED SALMONID FISH MORTALITY

Atlantic salmon (Salmo salar), sea trout (S. trutta m. trutta) and bro wn trout (S. trutta m. lacustris) at four fish farms in northern Finla nd were examined in 1988-1992 for external lesions with filamentous ba cteria. Phenotypic tests demonstrated that most of these bacteria were very similar to Flavobacterium johnsoniae. In two cases Flavobacteriu m columnare was isolated also. A total of 247 tanks (cases) with fish having external lesions containing filamentous bacteria were found, 57 .5% of which contained only filamentous bacteria, while the rest had s imultaneous non-filamentous bacterial or parasitic infection. In 31.6% of the cases more than 5% of the fish died in the course of the disea se, but in 39.7% of the cases no mortality occurred or it was below 1% . The disease symptoms occurred on either the gills, jaws, skin, fins or tail, or on different combinations of these. Logistic regression an alysis was used to assess the significance of the site of the symptoms , fish species, fish age, rearing density, other simultaneous infectio ns, water temperature and the farm for fish mortality in the cases wit h filamentous bacteria. The results indicated that water temperature, fish species, gill or jaw erosion and the farm itself had the greatest effects on mortality.