New case study: robust smolt

Understanding how freshwater environmental conditions impact fish health and performance

Scottish salmon farming is a cornerstone of the UK’s food industry, supplying 40% of Scotland’s food exports. As global demand grows, producers must expand sustainably while continuing to improve fish health. This project explored how freshwater rearing conditions - such as water chemistry, temperature, light cycles, and nutrition - affect salmon health and performance, focusing on differences between Recirculating Aquaculture Systems (RAS) and traditional open-water lochs.

The project partners were the Institute of Aquaculture, University of Stirling, University of Exeter, University of Aberdeen, Roslin Institute, Cefas, BioMar, Cooke Aquaculture Scotland, PHARMAQ, Bakkafrost Scotland (formerly the Scottish Salmon Company), Mowi Scotland, Scottish Sea Farms, and Grieg Seafood Shetland (now Mowi Scotland). The funder was UKRI, and the project was supported by SAIC. The total value was £1.7M.

The project examined factors influencing fish physiology, immune function, and microbiome development. Findings revealed that salmon raised in RAS environments show distinct physiological and genetic traits compared to loch-reared fish. For example, RAS fish had lower baseline immune activity but demonstrated strong immune responses when challenged. Microbiome studies highlighted dynamic changes in skin, gills, and gut, shaped by early freshwater exposure and tank conditions. The project emphasised the importance of early rearing conditions in breeding strategies.

The project’s findings are expected to inform industry practices that enhance fish health and immune function through early freshwater conditioning. These insights are crucial for developing new husbandry practices, health protocols and feeding regimes that support the sector’s sustainability goals.

This project strengthens the UK aquaculture industry by providing evidence-based strategies to improve fish welfare and productivity, ensuring a stable supply of nutritious, omega-3-rich salmon for consumers worldwide.

The full name of this project is ‘Understanding the impact of freshwater rearing environments on Atlantic salmon health and performance: Robust Smolt’

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