OCHROCONIS HUMICOLA CAUSING MUSCULAR BLACK SPOT DISEASE OF ATLANTIC SALMON (SALMO-SALAR)

A dematiaceous hyphomycete was isolated from black discoloured areas o f the somatic musculature of a specimen of Atlantic salmon. The fungus caused an endogenous mycosis and obviously must be classified as a fa cultative or opportunistic pathogen of marine fish. The optimum temper ature for the strain was in the range between 20 and 25 degrees C, and the temperature tolerance for growth ranged from 10 to almost 37 degr ees C. The morphological and physiological investigation revealed that the pathogen belongs to the genus Ochroconis de Hoog et von Arx, whic h is synonymous with Scolecobasidium Abbott. However, the definite spe cies identification raised some difficulties, because the characterist ics of our pathogenic isolate H 14 670 variably matched with at least four of the known species within the Ochroconis-Scolecobasidium-Dactyl aria complex, i.e., O. humicola, O. constrictum, O. gallopavum, and O. simplex. Because of this multispecies affinity and taking into accoun t the actual confused taxonomic state within this group of hyphomycete s, especially with regard to the pathogenic strains, the identificatio n of the present isolate as O. humicola remains with some reservation.