PHYSIOLOGICAL CHARACTERIZATION OF SAPROLEGNIA-PARASITICA ISOLATES FROM BROWN TROUT

Saprolegnia parasitica has caused large mortalities in brown trout, Sa lmo trutta, in Spain. Several strains of Saprolegnia parasitica have b een isolated from these epizootics and characterized regarding their p hysiological adaptation and genetic diversity. These isolates exhibit similar physiological characteristics, i.e. radial growth, zoospore mo bility and germination after encystment and differ substantially from other strains of the Saprolegnia diclina-parasitica complex tested. Ra ndom amplification of polymorphic DNA polymerase chain reaction (RAPD- PCR) of total DNA revealed a genetic similarity of about 85-100% betwe en Spanish trout isolates whereas only 20-45% similarity to other stra ins of the Saprolegnia diclina-parasitica complex was found. The resul ts suggest that the Spanish isolates are closely related strains and t hat they might have originated from one clone.