New case study: a vaccine against Rainbow Trout Fry Syndrome

Produce a novel vaccine against RTFS and test its efficacy in the field in Scotland

Rainbow Trout Fry Syndrome (RTFS) is a bacterial disease that thrives in cold waters below 15°C. It primarily affects young trout and has long been a challenge for aquaculture, causing early-stage mortality and economic loss. Currently, there are no commercial vaccines available in Europe or the UK, leaving antibiotics as the only treatment option - a solution that raises sustainability and resistance concerns.

Valued at £111k, the partners on this project were DawnFresh Farming, University of Stirling, Tethys Aquaculture, and Kames Fish Farming Ltd. The project aimed to develop and test a novel immersion vaccine for RTFS. Immersion vaccination is critical because fry are too small for injection and highly vulnerable to infection.

Researchers characterised over 300 bacterial isolates to select strains offering cross-protection and developed a vaccine that showed promising results in laboratory trials, achieving 84% relative survival and protection against multiple strains. To validate these findings, the vaccine was reproduced at a certified facility and tested in field trials at two Scottish trout farms. Fry were vaccinated by immersion and given a booster after 300 degree-days, with outcomes monitored during natural RTFS outbreaks.

Despite strong lab results, the immersion vaccine did not provide sufficient protection against circulating strains in real farm conditions. The complexity of RTFS, strain diversity, and challenges in vaccinating juvenile fish remain major hurdles.

The study highlighted the potential of mucosal vaccination, a method targeting gills, skin, and gut, which are natural entry points for pathogens. This approach reduces handling stress and could enable early protection for fry. Future research will focus on innovative delivery systems, mucosal adjuvants, and advanced techniques like epitope mapping and proteomics to design more effective vaccines.

While the initial vaccine was not successful in the field, this project provides critical insights and a roadmap for developing next-generation solutions to combat RTFS, improving fish health, reducing antibiotic use, and supporting sustainable aquaculture.

The full title of this project is ‘Developing a novel vaccine for prevention of Rainbow trout fry syndrome’.

Read the case study