But low stocks of wild salmon – especially the Atlantic variety native to our shores – means that over 70% today comes instead from fish farms, according to the Global Salmon Farming Resistance, an alliance of activists, NGOs and scientists.

These mighty and nomadic creatures, whose natural instinct is to swim freely for thousands of miles, are forced to spend their entire lives in captivity. The piscine equivalent of battery hens, they are born in hatcheries and then, at the “smolting” age, when they would normally migrate from the rivers of Scotland out to the North Atlantic Ocean, are confined to industrial-scale caged pens that, according to many experts, are breeding grounds for disease and cruelty.

Last month, the world’s leading producer of farmed salmon, Mowi, was stripped of its Royal Warrant – meaning its products will be off the table this year at Sandringham where the King (a life-long animal lover) and royal family traditionally gather for Christmas lunch.

The Royal Household does not comment on why companies are added or removed from its list, but the decision followed the emergence of filmed evidence captured by The Great Britain Foundation showing “systemic cruelty” – including fish being beaten to death – at Mowi’s Loch Harport site on the Isle of Skye.

The farm also had its RSPCA Assured (an animal welfare scheme) accreditation suspended. That has now been reinstated following an investigation and staff retraining, a spokesperson for Mowi told the Sunday Express. But the firm, which employs more than 1,600 people in Scotland and supplies the majority of the UK’s farmed salmon, has been in trouble before.

In May 2023, the Norwegian-owned company was fined £800,000 after admitting to health and safety breaches that led to the death of one of its employees, Clive Hendry, 58, who was crushed and drowned during a boat transfer.

Documents released under the Freedom of Information Act, as reported by the Scottish Daily Record, showed that anadditional 49 workers have sustained injuries – including amputations and broken bones – over the last five years.

The sheer density of salmon packed into these farms can also result in diseases and viruses sweeping through the pens, according to investigators from animal charities. The huge amount of excrement produced by the salmon, combined with uneaten food, sinks to the bottom, harming marine life by smothering the seabed. And it’s not just fish waste in the water either.

Video footage obtained by Animal Equality UK, a charity that champions the rights and welfare of livestock and fish in the food industry, appeared to show a worker at another fishery owned by Mowi urinating into one of the fish pens.

Abigail Penny is executive director of Animal Equality UK. She told the Express how investigators had also provided her with evidence captured on underwater cameras in many of Scotland’s fish pens, including Mowi and Bakkafrost Scotland.

“When you see the haunting footage we’ve captured, it’s hard not to believe that this is an industry blighted by contempt for animal, as well as human, welfare,” said Abigail. “Salmon trapped in underwater cages while they’re eaten alive by lice, blind, diseased, or deformed.

“And when you consider that every farmed salmon is typically fed hundreds of other wild-caught fish before it, too, is then eatenby humans, it’s painfully clear that Scottish salmon farming is far from luxurious and nowhere near sustainable.”

Last month, supermarket giant Tesco suspended orders from a Bakkafrost Scotland farm on Loch Torridon in the north-west Highlands based oncovert footage released by Animal Equality showing lice-infested salmon trapped in a pen that was supposed to be empty.

Bakkafrost Scotland’s spokesperson told the Express: “Six months ago, a very small number of fish were identified at our site on Loch Torridon, which had been declared fallow. We acted immediately to remove the fish, working with the relevant authorities.

“Following this, we undertook a comprehensive review of our procedures and implemented enhanced controls to ensure this does not happen again. At Bakkafrost Scotland, fish health and welfare are central to everything we do, and we remain committed to the highest standards of care and continuous improvement across operations.”

A spokesperson for Tesco said: “We take animal welfare extremely seriously, and we expect all our suppliers to adhere to our high welfare standards.

“As soon as we were made aware of this concerning footage, we immediately suspended the farm to carry out an investigation with our supplier. Any failure to meet our high welfare standards is unacceptable and we take swift action where necessary.”

As the world struggles to deal with the so-called “protein crisis” – the need to provide, in a sustainable manner, enough nutrition for a constantly growing population – fish is often touted as the more ecologically sound alternative to meat.

But is producing more fish at any cost really the answer? And is it actually sustainable or more healthy?

Many well-respected experts believe not.

Dr Shireen Kassam is a consultant haematologist and honorary senior lecturer at King’s College Hospital, London. She is also the founder and director of the non-profit Plant-Based Health Professionals UK.

“Farmed salmon does not deserve to be considered a health food,” she said. “Fish has conventionally been considered a healthy component of a diet, mainly because it is a source of long chain omega-3 fat. However, this does not consider the fact that farmed salmon now contains more saturated fat than wild fish, and lower amounts of omega-3 fats”.

An Australian environmental group found that a 200g serving of farmed salmon contains, on average, more total fat (though less saturated fat) than a Big Mac.

“In addition,” said Dr Kassam, “[farmed salmon] accumulates and exposes people to environmental pollutants, including microplastics, and to antibiotic-resistant strains of bacteria. All of these issues are beginning to raise concerns about the potential for negative impacts on health.”

A top US-based doctor, health author and president of the non-profit research and advocacy group Physicians Committee for Responsible Medicine, based in Washington DC, goes further still.

Neal D Barnard told the Express eating farmed salmon was akin to “smoking a low tar cigarette”. He continued: “Salmon is wildly over-hyped. It has huge drawbacks.

“For starters, it interferes with weight loss. That’s because it’s a very fatty fish, and most of that fat is not omega-3 ‘good fat’. Those fat grams are calorie-dense. As a group, fish eaters are significantly heavier than people who avoid fish and other meats. The same is true for diabetes risk. Like all carnivores, salmon accumulate toxins.

“In addition, the crowding on aquatic factory farms means that chemicals are often used to control parasites that spread from one fish to the next.”

So is the industry at least benefitting the local communities it operates in? Ailsa McLellan, a marine scientist from Wester Ross, in the Northwest Highlands of Scotland, says not.

“I worked on salmon farms after I graduated in marine science and then went on to audit farms for the RSPCA Assured scheme,” she said. I quickly realised there was no ethical or humane way to rear carnivorous, migratory fish in small cages.

“Living beside a salmon farm is like living beside any other industrial factory farm – polluting, cruel, noisy, smelly and invasive. Generators run constantly to power 24 underwater lighting at this time of year – the farmers say this is for welfare but it’s to manipulate the fish’s maturation and growth rates.

“During the warmer months generators run 24/7 noisy compressors to blast oxygen, as there isn’t enough naturally in the water to support the thousands of fish in the pens. There are noisy boats to-ing and fro-ing day and night, sucking fish on and off salmon farms to be treated for diseases andsealice, or culled.”

She continued: “The only good thing salmon farms provide are jobs and money, and that makes it very hard to criticise them as they inveigle their way into cash-strapped communities by providing sponsorship and handouts for schools and events.

“But the jobs are becoming fewer as the industry constantly strives for automation. As for money, these are foreign-owned multinationals that treat Scotland’s coastal seas as an open sewer while they extract as much profit for their shareholders as they can in the process.”

Mowi told the Express: “Mowi is rightly proud of its healthy and nutritious salmon and has been honoured to have held the Royal Warrant. Mowi does not comment on decisions made by the Royal Household.”

The company added that all of its Scotland farms are currently certified by the RSPCA Assured label scheme. Regarding its site at Lock Harport, Mowi added: “RSPCA protocol is toimmediately suspend sites whilst an investigation takes place. That investigation did take place andthe suspension was lifted from the site thereafter. All staff at all of Mowi Scotland’s farms receive regular refresher training to ensure they follow the strict requirements of the RSPCA welfare standard at all times.”

Salmon Scotland told the Express:“Anti-salmon farming groups like Animal Equality UK rely on spurious and unsupported allegations to push an agenda that would shut down salmon farms and put 11,000 Scots out of work.

“Farmers, vets and fish health professionals monitor fish daily and Scotland has some of the highest welfare standards anywhere in the world. Sea lice levels are at some of the lowest on record and survival rates are among the highest, backed by more than £1billion of investment in welfare and veterinary care.”

While the Scottish Government’s Fish Farm Production Survey quotes a figure of 1,362 employed, Salmon Scotland says that only counts marine staff, which is just a fraction of the sector’s total workforce.

They say independent analysis shows that salmon farming adds about £1billion a year to Scotland’s economy and is also the UK’s largest food export, worth £844million last year.

Whatever the figures, many top British chefs such as Hugh Fearnley-Whittingstall are taking industrially farmed fish off the table. The River Cottage, TV presenter and food writer told the Express: “I don’t use industrially farmed salmon at home or on our menu at River Cottage because I’m simply not confident it’s a sustainable product.

“The heavy use of prophylactic chemicals to treat these highly stressed fish; the pollution of the local marine environment from their faeces; and the unsustainable harvesting of wild fish to make the fish feed – it’s a triple whammy of environmental problems that are still a long way from being solved.”

Hugh has advice for Express readers looking, like him, to serve something kinder, healthier and more sustainable this Christ-mas: “I’d much rather eat, and serve to my guests, locally landed wild fish caught by small scale inshore fishermen, or locally farmed shellfish such as mussels and oysters that come from a much cleaner and more sustainable type of aquaculture.

“And of course, whenever given the chance, I’d encourage anyone buying fish to eat at home to follow the same course.”