Ingunn Sommerset, Department Director for Fish Health and Welfare at the Norwegian Veterinary Institute, and Torfinn Möldal, Fish Health Manager and editor of the report.
Photo: Veterinærinstituttet.
Infectious diseases and injuries from sea lice treatments continue to pose significant threats to Norwegian farmed salmon, according to the newly-released 2024 Fish Health Report from the Norwegian Veterinary Institute (Veterinærinstituttet).
While overall mortality in 2024 declined slightly compared to 2023 - a crisis year, when Norway recorded its highest-ever mortality rate for sea phase salmon - veterinary experts warn that serious fish health and welfare challenges persist.
Ingunn Sommerset, Acting Director of Fish Health and Welfare at the Norwegian Veterinary Institute said in a statement that "injuries as a result of sea lice treatments, wound problems and gill disease are the biggest challenges".
She added that although there was some "positive development" for several viral diseases, "some bacterial diseases for which there are no good vaccines have had a negative development", and thus must be closely monitored.
According to the report, 57.8 million salmon died during farming in 2024, a reduction from 62.7 million the previous year, with the estimated overall mortality for farmed salmon in the sea phase standing at 15.4%, down from 16.7% in 2023.
However, mortality in fish hatcheries reached its highest recorded level for fry (over 3 grams), with the Institute reporting that 45.8 million salmon and 3.4 million rainbow trout died in 2024 - the highest number since these data became available.
Norwegian Veterinary Institute data show that infectious diseases accounted for 33% of salmon mortalities at reporting sites. Injuries, which were primarily linked to intensive lice treatments, represented 27%, followed by unknown causes (21%) and environmental conditions (9%). Notably, environmental factors such as jellyfish blooms played a larger role in 2024 than in the previous year, especially in Northern Norway.
The report provides further details of the incidence of infectious diseases, showing that the number of confirmed cases of both pancreatic disease (PD) and infectious salmon anemia (ISA) declined or remained below the ten-year average.
Gill disease, exacerbated by various pathogens and environmental stressors, remains a major concern and contributes significantly to fish mortality. Meanwhile, bacterial winter sores remained widespread in salmon farms, the report found.
The Norwegian Veterinary Institute also highlights that outbreaks of pasteurellosis, once concentrated in Western Norway, were recorded in Northern Norway for the first time in 2024, and reports of piscirickettsiosis increased, with the disease identified at multiple sites in Northern Norway - an escalation likely linked to warming waters caused by climate change.
"The detections of piscirickettsiosis are probably related to high sea temperatures. If sea temperatures continue to rise, there is a risk that bacterial problems in general will increase in scope," said Torfinn Moldal, editor of the Fish Health Report.
Higher sea temperatures are also linked to a proliferation of parasites impacting farmed fish.
The report shows that sea lice continue as one of the most significant problems affecting fish health and welfare, with lice numbers increasing sharply toward the end of 2024. Warmer sea temperatures, especially in Central and Northern Norway, and greater fish biomass likely contributed to higher lice levels, the Institute said.
Sea lice were the root cause of a significant propotion of injuries and mortalities, due to mechanical and thermal de-lousing treatments, underscoring the need for gentler solutions to improve fish welfare, the Institute said, noting that more delousing procedures were carried out in 2024 than in 2023. The survey found that delousing-related injuries ranked highest as a cause of reduced welfare in salmonids, with gill disease and jellyfish ranking as joint second.
