Scottish Sea Farms has reported lower levels of the parasite in 2024 compared to the previous year © Scottish Sea Farms
Survival rates returned to 90 per cent, up from 82 per cent in 2023, the company observed in their latest newsletter, thanks in part to cooler seawater temperatures which led to better biological conditions and improved gill health.
The company also reports a substantial increase in harvest volumes, reaching 40,400 tonnes, up from 24,900 tonnes in 2023, and higher harvest weights.
“We’re back to where we should be but we’re not complacent,” said Scottish Sea Farms' head of fish health and welfare, Ralph Bickerdike.
“We certainly learned from the challenges of 2022-23 and have reviewed all our operations, but we want to see even higher survival,” he added.
According to the company, their breeding programme, which takes place in collaboration with AquaGen Scotland, has produced more robust broodstock.
“It takes three years to get fish up to broodstock size and the first crops from these fish, harvested in 2024, did really well. Every year we’re selecting fish from our farms which will then be used for broodstock. Hopefully, by doing this over successive generations, we will see even more improvement in the climate resilience of our fish,” said Bickerdike.
Feeding was also reviewed and diets altered to help meet the seasonal nutritional requirements for health and welfare.
“We worked with our feed supplier to adapt the composition of the feed in Q3, when fish health is most likely to be compromised, and the early results are very encouraging,” explained Bickerdike.
Temporary feed withdrawal during times of challenge as mitigation further contributed to survival, by keeping fish away from the surface when harmful jellyfish and plankton were in the water.
Technological advances in the supply chain also contributed, enabling earlier detection of disease and quicker interventions.
“We’ve been evaluating the latest underwater biomass cameras, which monitor individual fish for weight estimation and assess the condition of the fish without us having to handle them. They can give us real-time indications of welfare parameters, which we can then investigate and act on if necessary,” said Bickerdike.
And the use of modern diagnostics, such as PCR swabs for amoebic gill disease (AGD), has led to better informed treatment decisions, as have daily water sampling and surveillance, which provide a timely record of environmental changes.
