Health of farmed salmon in Norway: "both good and bad news in 2024", say experts

While pancreatic disease has declined, bacterial kidney disease has seen a resurgence of outbreaks, which pose a significant risk to both farmed and wild fish, according to the Norwegian Veterinary Institute's latest report.
Pancreatic disease reduces growth in farmed salmon. Pictured: a healthy farmed salmon above, compared with one with pancreatic disease below, where both are the same age.

Pancreatic disease reduces growth in farmed salmon. Pictured: a healthy farmed salmon above, compared with one with pancreatic disease below, where both are the same age.

Photo: Trygve Poppe / Norwegian Veterinary Institute.

In 2024, the Norwegian farmed salmon industry has seen some improvements in fish health, but significant challenges remain, according to the Norwegian Veterinary Institute's latest report.

The report focuses on three major diseases affecting farmed salmon and trout in Norway: pancreatic disease (PD), bacterial kidney disease (BKD), and infectious salmon anemia (ISA) - the last of which has seen a spate of infections in recent weeks, with a series of suspected and confirmed cases reported to Norwegian authorities.

Promising decline in Pancreatic Disease

Pancreatic disease (PD), a serious viral infection affecting farmed Atlantic salmon and rainbow trout, has shown a notable decline, the Veterinary Institute reports.

"This disease creates major welfare challenges for the fish and accounts for major losses for the farming industry in the form of poor growth and reduced slaughter quality. The fact that we have seen a decrease in cases of disease in the last four years, and that the trend seems to continue, is very positive," said Ewa Harasimczuk, subject officer for fish health at the Veterinary Institute, in a media release.

According to the Veterinary Institute, cases have decreased significantly over the past four years. In 2020, there were 158 reported cases, dropping to 58 in 2023. This year, only 22 suspicions have been reported, with 15 confirmed cases, marking the lowest incidence since 2005.

Harasimczuk attributes this positive trend to increased vaccination and fewer infected fish in the sea.

Infectious Salmon Anemia at expected levels

Meanwhile, cases of Infectious salmon anemia (ISA), another severe and contagious disease, continue to be detected in Norway - although at "expected levels", the Institute says.

ISA affects the fish's blood vessels, leading to anemia and circulatory disorders.

This year has seen nine confirmed cases and eight suspected cases, comparable to the same period last year, which recorded 11 confirmed cases, the Institute notes.

Resurgence in Bacterial Kidney Disease, with risk to wild fish

However, Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum, remains a significant challenge in Norway, the Institute says.

This chronic disease, which currently has no effective vaccines or treatments, saw a resurgence in 2023 with 12 outbreaks. So far in 2024, five outbreaks have been reported, primarily in production area 6, between Nordmøre and Sør-Trøndelag.

The disease is believed to be spread by movement of wellboats and fish transport, the Institute says.

However, the bacterial disease is highly transmissable, and can also be passed on in breeding facilities, Harasimczuk warns: "Good control of broodstock production is necessary because the bacteria can be transmitted via fertilized eggs from mother to offspring."

The Veterinary Institute notes that the pathogen which causes the disease, Renibacterium salmoninarum, has not been detected in wild fish since 2019.

However, it warns, "the situation may change as a consequence of the escape of infected fish from Reitholmen in Hitra municipality. Of the recaptured fish, four have tested positive for BKD".

In May, Lerøy Seafood Group reported a fish escape from its Lerøy Midt Reitholmen operation in Hitra, Norway, after BKD had already been detected among fish at the facility.

As of May 20, the company had caught about 1,200 of the estimated 8,400 escaped farmed fish through its recapture efforts in the area of the escape, according to the Norwegian Directorate of Fisheries.

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