The salmon farming industry, which produces Scotland's biggest food export, is coming under new scrutiny as use of antibiotics has soared in four years as use elsewhere slumped.

Analysis produced by Salmon Scotland accepts that 8.9 tonnes of drugs with an antibiotic ingredient were used in 2021, over two-and-a-half times more than when data was first published in 2017.

Meanwhile, use in other food-producing species such as turkeys and chickens has slumped.

In 2017, the World Health Organisation was recommending that farmers and the food industry stop using antibiotics routinely to promote growth and prevent disease in healthy animals.

The WHO recommendations aimed to help preserve the effectiveness of antibiotics that are important for human medicine by cutting their unnecessary use in animals.

At that time, in some countries, approximately 80% of total consumption of medically important antibiotics is in the animal sector, largely for growth promotion in healthy animals.

It warned then that over-use and misuse of antibiotics in animals and humans is contributing to the rising threat of antibiotic resistance.

While salmon use of antibiotics has soared trends compiled by the animal industry on a voluntary basis for the Veterinary Medicines Directorate shows that usage has plummeted with other animals since it was first analysed.

According to directorate data use in ducks has dropped by 89% since 2014, in turkeys it is down 81% since 2014, in broiler chickens there's been a drop of 72%, in trout and pigs there has been a decline by 69% since 2017 and 2015 respectively, in game birds the dip is 55% since 2016 and in laying hens, there has been a 50% slump.

Salmon Scotland said that the cattle and sheep industry - which is significantly larger- does not publish any antibiotic figures - and so the analysis is an "incomplete" picture of all farming. It also said that the pig farming sector uses double the amount of antibiotics of salmon farming.

The most used antibiotic used by the Scots salmon industry is Oxytetracycline accounting for 86% of total use.

Salmon is Scotland’s single biggest food export – worth over £600 million – and is estimated to support 12,000 jobs and 3,600 suppliers in Scotland.

International sales of Scottish salmon were valued at £280m in the first half of 2022 alone, and the industry has said it is on course for record exports this year.

Campaigners have been pushing for fish farm companies to end the drug dependency and for tougher regulation of salmon farms.

Four years ago, a Scottish Parliament rural economy and connectivity committee inquiry into salmon farming in Scotland stated that effective regulation of medicine used by the farmed industry was a "requirement" after noting with "concern" that research by the Scottish Environment Protection Agency that medicine from Scottish salmon farms "is significantly impacting local marine environments.

Edward Mountain, the Highlands and Islands MSP who was covener of the committee at the time of the inquiry said that the directorate analysis indicates how "every other livestock producer is doing all they can to tighten up usage of antibiotics, except for the farmed salmon industry whose usage is rocketing".

He added: "Even with spiralling mortalities, the farmed salmon sector is pumping 8.9 tonnes of antibiotics into the sea – an astonishing amount.

“One really has to question if this is something Scottish food producers are happy to be associated with?”

Salmon Scotland, in its analysis for the directorate insisted that antibiotic treatments were "still relatively infrequent in the salmon farming sector" with only 8.5% of freshwater farms and 4.9% of marine farms treated in 2021.

It says it is therefore not routinely used.

"Antibiotics are only ever used in response to the clinical presentation of bacterial infection: there is no prophylactic use of antibiotics, and any use is supported by

appropriate sensitivity testing," the group said.

"The salmon sector continues to focus on a holistic and preventative approach to health management, including vaccination, antibiotic stewardship, biosecurity and health and welfare planning.

"The sector remains committed to responsible use of antibiotics, balancing a drive to reduce use against the need to safeguard fish health and welfare."

It comes as the industry has come under fire for "sickening" record levels of fish deaths, four years after coming under parliamentary scrutiny over its record.

Calls have been made for a fresh inquiry as "alarming" figures show the amount of fish destroyed by diseases and other issues at farms is even higher than "stomach-churning" levels that led to calls for a moratorium on the expansion of the salmon farming sector.

Analysis of official figures reveals that the amount of destroyed fish on farms has risen three-fold in eight years with nearly 29,958 tonnes - nearly 13 million fish - being thrown away in 2021.

Four years ago, when MSPs were examining the industry, there were nearly 2m (4515 tonnes) fewer fish dying.

In 2017, a systematic review published in Lancet Planetary Health found that interventions that restrict antibiotic use in food-producing animals reduced antibiotic-resistant bacteria in these animals by up to 39%.

This research directly informed the development of WHO’s guidelines.

"Scientific evidence demonstrates that overuse of antibiotics in animals can contribute to the emergence of antibiotic resistance," said Dr Kazuaki Miyagishima, director of the department of food safety and zoonoses at WHO in announcing the guidelines.

"The volume of antibiotics used in animals is continuing to increase worldwide, driven by a growing demand for foods of animal origin, often produced through intensive animal husbandry.”

Salmon Scotland pointed out that the turkey sector has seen a rise in antibiotic use by 16.8 from 2020 to 42.6mg/kg in 2021.

Dr Iain Berrill, head of technical at Salmon Scotland, said: “Like any medicine, antibiotics are used responsibly, sparingly and only when required in the health and welfare interests of our fish, and only under prescription from licensed veterinarians.

“2021 was a record year for salmon production, with more fish in the water for longer due to the loss of markets as a result of Covid. The requirement to protect our fish from environmental challenges meant antibiotics were used on a small number of farms. We are committed to reducing use as low as possible.”