Mowi Scotland reports major improvements in fish health and survival rates
Mowi Scotland has reported a significant decline in fish mortality rates in 2024, citing improved biological conditions, enhanced biosecurity, and advances in preventive health strategies. The company recorded a 35% reduction in overall biomass mortality across its seawater farms compared to the previous year, with mortality in terms of individual fish numbers down by 45%.
The improved outcomes were attributed to a combination of targeted health interventions and more favourable environmental conditions, including lower water temperatures and increased rainfall during the summer months.
Advances in vaccination and biosecurity
Preventive health measures have played a key role in the improved performance, with Mowi Scotland introducing new vaccines in recent years to mitigate disease risks. The company reported that its autogenous vaccine programme—developed in collaboration with Ridgeway Biologicals—has significantly reduced clinical outbreaks of Pasteurella skyensis and Yersinia ruckeri.
“We continue to prioritise vaccination as a core part of our fish health strategy,” Mowi Scotland said, noting that further vaccine developments are underway, including efforts to combat Piscirickettsia salmonis, which causes salmonid rickettsial septicaemia (SRS).
Biosecurity measures have also been strengthened across Mowi Scotland’s operations, with enhanced filtration, disinfection, and water treatment technologies deployed across its well boat fleet. The company highlighted ongoing research into bacteriophage therapy—viruses that target harmful bacteria—as a potential alternative to antibiotic treatments.
Sea lice and gill disease control
Parasitic challenges, particularly sea lice and amoebic gill disease (AGD), were another focus area in 2024. Mowi Scotland reported the lowest sea lice levels in more than a decade, alongside a 56% reduction in mortality related to AGD and other gill infections.
The company attributed these improvements to investments in non-medicinal treatments, including the use of freshwater baths, mechanical delousing, and ozonation systems on well boats. The deployment of cleaner fish to manage sea lice populations has also played a role in reducing dependency on medicinal treatments, with bath treatment medicine usage down by 60% in 2024.
Mitigating jellyfish threats
Jellyfish and harmful plankton blooms have become an increasing challenge in Scottish waters, prompting Mowi Scotland to trial new protective measures. In 2024, the company tested bubble curtains—already used in Mowi’s Chilean and Canadian operations—to create physical barriers against plankton. Early results suggest these methods are effective in preventing damage to fish gills.
Alternative mitigation strategies include temporary feed withdrawal, reducing fish exposure to surface waters where jellyfish concentrations are highest, and deep-welling aeration systems.
Expansion of breeding and post-smolt production
Mowi Scotland has also taken steps to enhance the resilience of its fish stocks through selective breeding. In 2024, the company produced 20.5 million green eggs using its own Mowi salmon strains, with a new breeding facility in Ardessie set to open in 2025. The company expects the facility to produce up to 50 million eyed eggs annually, reducing reliance on external suppliers.
A post-smolt strategy launched in Loch Etive in 2024 has also yielded promising results, with fish spending less time at sea before harvest, reducing exposure to environmental risks.
Research collaboration with University of Edinburgh
Looking ahead, Mowi Scotland has partnered with the University of Edinburgh on a five-year research initiative to further improve fish health and survival rates. The programme, SalmoStrong, will recruit PhD students and postdoctoral researchers to study genetic diversity, early rearing practices, and new breeding techniques aimed at producing more resilient fish.
While the company has made significant progress in reducing mortality, it acknowledges that further improvements are necessary to meet long-term sustainability and welfare targets.
“Investment in people, innovation, and adaptation remains critical to improving fish health outcomes,” Mowi Scotland said.
The company currently operates 59 farms across freshwater lochs, land-based hatcheries, and open-sea sites in Scotland.
