Identification of Saprolegnia Spp. Pathogenic in Chinook Salmon : Final Report.

This project has developed procedures to assess the role of the fungal parasite, Saprolegnia in the biology of salmon, particularly adult Chinook, in the Columbia River Basin. Both morphological and DNA ``fingerprinting`` surveys reveal that Saprolegnia parasitica (=S. diclina, Type I) is the most common pathogen of these fish. In the first phase of this study 92% of 620 isolates, from salmon lesions, conformed to this taxa of Saprolegnia. In the current phase, the authors have developed variants of DNA fingerprinting (RAPD and SWAPP analysis) that permit examination of the sub-structure of the parasite population. These results confirm the predominance of S. parasitica, and suggest that at least three different sub-groups of this fungus occur in the Pacific N.W., USA. The use of single and paired primers with PCR amplification permits identification of pathogenic types, and distinction from other species of the genus considered to be more saprophytic in character. A year`s survey of saprolegniaceous fungi from Lake Washington indicated that the fish-pathogen was not common in the water column. Where and how fish encounter this parasite can be approached with the molecular tags identified in this project