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New case study: Rainbow Trout Fry Syndrome (RTFS) and disease resistance in salmon and trout

To identify genetic markers linked to natural resistance against F. psychrophilum in Atlantic salmon

Rainbow Trout Fry Syndrome (RTFS) has caused significant losses in trout farming worldwide for decades. The same bacterium has been found in Atlantic salmon fry in Scotland. The disease, triggered by the bacterium Flavobacterium psychrophilum, leads to skin damage and mortality in young fish. With no vaccines available in the UK, farmers rely on antibiotics to control outbreaks, increasing the risk of antibiotic resistance. This makes alternative solutions, such as selective breeding and vaccine development, a priority.

This project aimed to identify genetic markers linked to natural resistance against F. psychrophilum in Atlantic salmon. These markers were then used to select parent fish to produce eggs with improved disease resistance. Researchers examined whether RTFS-resistant trout were more vulnerable to other major diseases. Valued at over £827k, the project was led by AquaGen Scotland, with partners from the University of Stirling, Cooke Aquaculture and Dawnfresh Farming. The project was supported by SAIC.

The project team:

  • Developed a controlled ‘challenge model’ to test salmon families for susceptibility to RTFS.
  • Collected samples from resistant and susceptible fish to identify genetic markers.
  • Produced salmon eggs with enhanced resistance.
  • Planned farm trials to validate results.
  • Assessed RTFS-resistant trout for susceptibility to other diseases.

The project created and applied a reliable RTFS challenge model for Atlantic salmon and identified two strong genetic regions (QTLs) linked to RTFS resistance, with the findings being used by AquaGen to produce salmon eggs with improved resistance. The case study notes that the challenge model can also aid future vaccine development and research into other diseases.

Additional benefits included new diagnostic tools for detecting F. psychrophilum and the discovery of a resistance marker in Rainbow trout, further improving breeding programmes.

The full title of this project is ‘Improving disease resistance in Atlantic salmon and Rainbow trout to Flavobacterium psychrophilum’.

Read the case study