Vaccinating salmon: how Norway avoids antibiotics in fish farming
Norway has cut antibiotic use in salmon – one of the principal foods consumed in the country and a major export – to virtually zero. This has led to a flourishing industry and a reduction in the risk of antibiotic resistance in humans.
Antibiotic use in fish farming
In the 1980s, Norway and other northern countries with plentiful fresh- and sea-water resources experienced an explosion of salmon farming. Formerly, salmon was a delicacy only a privileged few could enjoy. With the advent of fish farming, this tasty fish that is also rich in heart-healthy fats became available worldwide at much more affordable prices.
"It was an exhilarating time, but we also began to encounter some serious problems," says Mr Alf-Gøran Knutsen, General Manager at a family-run fish farming company that began its operations in 1976.
The main issue was that thousands of farmed salmon were affected by furunculosis, a bacterial fish disease also present in wild salmon. "There were no vaccines that worked well against furunculosis, and the conventional wisdom at that time was that it would be extremely difficult to produce one that was effective," recalls consultant and veterinarian Dr Paul Midtlyng, who was an officer for fish health in the Norwegian Ministry of Agriculture during the 1980s.
Along with other fish farmers, Mr Knutsen began mixing antibiotics into his fish feed to prevent and treat furunculosis in the late 1980s. "At the time, we were told this was the right thing to do. But in retrospect, we can see that it was a potentially dangerous practice," he says.
Risks of antibiotic overuse – and the alternative
"Overuse of antibiotics – in farming or for human medical treatment – speeds up the development of antibiotic resistance, when bacteria change and become resistant to the antibiotics used to treat the infections they cause. This is compromising our ability to treat infectious diseases and undermining many advances in medicine," says Dr Danilo Lo Fo Wong, Programme Manager, Control of Antimicrobial Resistance at WHO/Europe.
In the late 1980s, recognizing the urgent need to support Norway's robust fish farming industry without endangering public health, scientists at the Norwegian Veterinary Institute succeeded in developing an effective vaccine against furunculosis in farmed Norwegian salmon that has no side effects in humans.
By 1994, fish farmers across Norway had made the switch from antibiotics to vaccination. The vaccine is injected into the abdomen of salmon during their fresh-water phase using an automated process.
"This achievement was the result of a strong collaboration between government, farmers, industry and the fish farming association," Dr Midtlyng says. "All parties involved recognized that they could not continue using massive amounts of antibiotics." In short, business simply could not continue as usual.
"Norway's story illustrates how innovation and partnerships across many sectors of society are needed to protect the precious resource of antibiotics. This kind of collaboration represents a cornerstone of the WHO global action plan to tackle antimicrobial resistance," says Dr Marc Sprenger, Director, Antimicrobial Resistance Secretariat at WHO.
Other measures to prevent infection
Today, Norway produces 300 000 farmed salmon per year, and some companies vaccinate the fish on an industrial scale. Vaccination is now proven to have huge benefits for preventing infection. "However, a single strategy is not enough," says Dr Bjørn Røthe Knudtsen, a specialist on fish disease who works in the Norwegian Government's food safety division.
"Over time, Norway's fish farmers have introduced additional methods for good hygiene," he says. "Ideally, a single generation of fish should be kept in each site. If that's not possible, farmers periodically empty holding areas for fish, disinfect them and leave them empty for a few months. Such methods help prevent cross-contamination between old and new generations."
Benefits of safe fish farming
These different techniques have resulted in a sustained reduction in the use of antibiotics in Norwegian salmon farming. "Today, Norway has the largest tonnage of farmed salmon in the world and probably the lowest use of antibiotics," Dr Midtylng says.
Considering the arithmetic, he adds, "Norway's people use roughly 50 000 kg of antibiotics a year. In salmon, we are using only 1000 kg altogether to treat sickness, even though the salmon population has twice the biomass of human beings in our country."
As a businessman who is also concerned about health and the environment, fish farmer Mr Knutsen is highly pleased with changes over more than 3 decades. "We have achieved a combination of good farming business and responsible use of antibiotics," he says.
