Exploring genetic diversity and virulence variation among Saprolegnia parasitica isolates

Fish with saprolegniosis symptoms,  including white  cotton wool-like patches on infected skin along fish body and gills and fins.
Photo: Anna Cronheden

Saprolegnia parasitica is a freshwater pathogen that infects wild and farmed fish species worldwide, causing a devastating disease called saprolegniosis. Particularly severe outbreaks of saprolegniosis with massive losses are occurring in salmonid aquaculture. Saprolegniosis is characterized by white or grey cotton wool-like patches that cover infected skin lesions along fish body and gills and fins. With re-emerging outbreaks and without effective treatment, saprolegniosis remains a major problem for freshwater fish health and welfare. Monitoring the pathogen genetic diversity and virulence across outbreaks is hampered due to scarce genomic data and limited diagnostic methods. 

Funded by the Helge Ax:son Johnsons foundation, this project aims to generate whole-genome sequences by applying long-read sequencing of DNA samples from several S. parasitica isolates. Compared to short-read technologies, long-read sequencing achieves better resolution of repeat-rich regions and enables assembly of high-quality genomes. Generating such genomic resources would facilitate assessment of genetic diversity and virulence variation among S. parasitica  isolates and contribute to development of molecular diagnostic tools, improving monitoring of saprolegniosis
infections.