THE waters of Loch Fyne are still and calm, barely a ripple atop the glassy surface. It's late morning and the only movement comes from the occasional splash of sea trout jumping and a lone heron which glides to land on the seaweed covered, pebble-strewn shore.

At the oyster farm near the head of the loch, work has been underway for hours as the prized molluscs are sized, sorted and packed for delivery to Scotland's top restaurants and across Europe, the Far East and the Caribbean.

A spiralling grey plume rises in the distance from the smokehouse chimney. Here fresh salmon are filleted, hand-cured and smoked to be served in high-end venues around the world, including luxury hotel Burj al Arab in Dubai, the F1 Paddock Club and British Airways first class.

This year marks the 40th anniversary of Loch Fyne Oysters which was the brainchild of landowner Johnny Noble and marine biologist Andy Lane in the mid-1970s. The business has grown from humble beginnings, its assets valued at just £100, to a £16million annual turnover.

Next weekend a celebration, Fyne at Forty, will include a performance by Hue and Cry alongside a ceilidh, chef demonstrations, tastings, oyster shucking displays and a behind-the-scenes tour.

First let's rewind to the beginning: a story packed with maverick flair and derring-do. Noble was the owner of Ardkinglas Estate near the Argyll village of Cairndow, which he had inherited – along with considerable debts – from his father in 1972.

Lane, meanwhile, was working on a nearby salmon farm, diving to the bottom of the cages and picking out dead fish. Home was a ramshackle caravan with a leaking gas stove and roof light that frequently blew off in the wind.

Neither men had two pennies to rub together, but what they did have was ambition and fearless verve in abundance. When Lane suggested growing oysters, Noble was instantly enthused.

Lane, 66, fondly recalls how their adventures in oysters first took shape. "I was keen to work for myself and wanted to go into shellfish farming and got talking to Johnny about it," he says. "It struck a chord with him.

"He had been in the wine business dealing with single vineyards in France. He loved anything that was hand-produced or artisan. The whole oyster thing chimed with him."

They pooled their resources to get the business up and running. Lane chuckles at the memory of that fledgling operation.

"Johnny had a wooden mackerel boat that he put in as collateral and I put in a wetsuit and dinghy with a hole in it – those were the assets of the company. We kept quiet about the hole. The trick was to sit slightly to one side, so the water didn't come in."

It would consume their lives in those early years. Lane remembers working "daft hours", often starting at 5am and keeping going until midnight.

"You would do an early tide about dawn for the oysters, then go up to begin smoking the fish while somebody would rush off down to Crinan to pick up the prawns. You would catch the second tide of the day, then put all the orders on the train at Arrochar to go to London.

"After that we would start pickling herring. We used to pickle the herring in this terrible stuff called Don Pablo sherry. After the working day ended, sometime around midnight, we would drink it to wind down a bit. All the craic happened over the Don Pablo."

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Originally from Northamptonshire, Lane moved to Scotland at 19 to attend Stirling University where he studied biological science. A rugged life on Argyll's Cowal peninsula was what he had always aspired to.

"It was a lot of hard work, but a Boys' Own dream in a way," he says. "It was so wonderfully wild in those days. I never ever expected to prosper from it – I thought it was just going to be a good way of life.

"When you are growing shellfish, it takes years to get a return and you live on air in between. The margins are very low, so you must find something else to do. We went into smoking fish as well as buying and selling prawns. That, ultimately, was the trigger to more success."

To those outside looking in, the pair must have seemed an unlikely double act. Yet, one of the great strengths of their dynamic, says Lane, was that he and Noble were so starkly different.

"I think that's why we got on so well," he says. "The great common currency was laughter. Johnny was a very genial and funny man. He was great with people and entertaining. I enjoyed working on the shore and all that side of it. We met in the middle over ideas."

On one memorable occasion at a posh party in London, Noble was keen to disprove the old adage that oysters and spirits should never be mixed. The shellfish was duly served with vodka as he declared: "Either everyone will enjoy themselves – or everyone will chunder."

Lane chuckles when reminded of the story. "Johnny was always up for that kind of challenge," he says. "He had a very low tolerance of food snobbery and that kind of nonsense. We had both been to France and saw the way they treat their food – it is food for everyman.

"We wanted to sell oysters, mussels and smoked fish but make them accessible, so everyone could eat them. That was the philosophy behind it all.

"The estate gave us an apparent substance and credibility that belied the facts because it was a real shoestring operation kept together by hope, enthusiasm and good people."

At that time, the facilities were crude to say the least. Lane recounts the good-natured mayhem that ensued one day when an important customer showed up.

"There was a ruined house in the woods at Ardkinglas surrounded by rhododendrons," he says. "We worked in the old kitchens of that which sounds better than it was. It was very basic. We had been sending our prawns down to London and one day a major customer turned up unannounced.

"The estate office had tipped us the wink he was there and we thought there was no way he could see these primitive conditions. We shut the place up and all went off to hide in the rhododendrons.

"Thankfully dear old Johnny came down, took him back to Ardkinglas House and gave him something a lot better than Don Pablo sherry."

Having moved into smoked salmon, mussels, langoustines and other seafood delicacies sold through mail order, Noble and Lane set up an oyster bar in 1980.

What began as simply an umbrella and trestle table in a layby off the A83, moved into nearby farm buildings and underwent several incarnations before evolving into the swish restaurant purveying plump oysters and other dishes we know today.

Did they imagine the business would enjoy such success? "I didn't think much into the future," admits Lane. "All I wanted to do was grow shellfish because I loved the life. Johnny was ever the optimist. He was a very positive thinker, so he probably saw the future in grander terms.

"In the end, it became very successful and I suppose then you have to start behaving like a grown-up. Things like getting your systems organised which doesn't exactly get the pulses going."

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After Noble died in 2002, Lane was instrumental in ensuring that Loch Fyne Oysters was bought over by its employees before he himself left two years later.

"A huge regret is that didn't carry on and a lot of the blame is down to myself," he says. "It just seemed the most appropriate thing. Johnny was gone, he was such a huge character, and how do you replace him?

"The employee ownership should have worked but I didn't stay on long enough to help it work. For one reason or another it didn't quite gel which was a shame. But the company is still there."

Loch Fyne Oysters was taken over by Scottish Seafood Investments in 2012. Today the managing director is Cameron Brown who joined three years ago. His previous roles include overseeing rollmop herring production for the Macrae Food Group and a stint as managing director of Strathaird Salmon.

Brown, 53, describes Loch Fyne Oysters as "the most complex business" he has been involved in thanks to its numerous product and sales streams including the restaurant and delicatessen, smokehouse, its famed oysters, Hebridean mussel farm at Loch Roag and an online shop.

It is worth pointing out that the 32-strong chain of Loch Fyne Seafood and Grill branded restaurants around the UK has been owned by brewer Greene King since 2007.

"We are completely different entities," says Brown. "We have our own single restaurant here – the 'mothership' – and the other 32 are owned by Greene King."

Turnover at Loch Fyne Oysters is £16m each year, with the lion's share – £10m – coming from its smokehouse and salmon products. It is Brown's goal to grow the turnover to at least £25m within the next three to five years.

Brown is sanguine when asked what makes the oysters so special. "There is a lot of rainwater here," he says. "The River Kinglas and River Fyne flow into the top end of the loch and it sometimes makes the water not quite as salty as most sea sites.

"We have customers in Hong Kong who are so attuned to our oyster that they know when we have had quite a lot of rainfall because they can taste the difference. They will say: 'You guys had some pretty bad weather?' They can tell because the oysters aren't as salty."

Down at the farm, the team are hard at work getting the latest orders packaged. The company sells two million oysters annually, equating to around 40,000 a week. Some of the names on the boxes are instantly recognisable such as "Rogano" and "Crabshakk".

Iain MacKay, 44, from Inveraray has worked for Loch Fyne Oysters for 25 years. He started in the smokehouse and is now aquaculture manager.

He points to the loch where, at low tide, up to a thousand metal frames are visible, each one strung with a row of oyster-filled baskets.

The seed oysters are brought from the company’s hatchery and nursery in Morecambe Bay, Cumbria, to be grown at Loch Fyne or partner farms around the islands and west coast of Scotland.

"From seed to market takes about three years," says MacKay. "They sit in the water and feed off the natural plankton. We need to come down and shake the baskets and do that for each spring tide, every two weeks between a new moon and full moon. There are hundreds of frames, so you do it over several tides."

What are the signs of a good oyster? "You are looking for an almost stunted oyster, a small and fat one," he explains. "You don't want them getting too elongated. If they are nice and short and fat, then you know there is plenty of meat."

Seeing off the last of the morning's orders is dispatch and depuration manager Andre Hughes, 52, from Dunoon.

He demonstrates how to tap the oysters together to check if they are healthy before they are sent to customers.

A sharp sound like two stones being hit together is good, while a hollow clunk – a bit like coconut shells colliding – means the oyster has lost its fluid and is dead or dying. These are then discarded.

Inside a vast warehouse are depuration tanks where the oysters are filtered to remove any potential bacteria, viruses and toxins. The shellfish have already been sorted by weight, the smallest around 65-75g and the largest upwards of 120g.

Hughes plucks one from a tank. "I love oysters, but I would not thank you for something that size," he says. "The 120g plus is a big oyster. They are used more for cooking, such as making sauces."

It's not a case of the bigger the better? "Definitely not," says Hughes. "If I was eating oysters I would want the smaller sizes. I don't think the taste changes that much, it is more about the volume. You want to be able to swallow it in one."

He is a big oyster fan which is surely a perk of the job. "I eat them on at least a weekly basis," he says.

"My absolute favourite is to have them raw, sometimes with lemon juice or Tabasco sauce, maybe a bit of vinaigrette. Sometimes I will bake them. I'm always trying to introduce people to shellfish and would do anything to get people to eat it."

Not everyone is enthusiastic. "The number of horrible things I have heard said about oysters is enough to put people off straightaway," says Hughes, with a frown. "I want to get away from that mindset. In Europe – France, Spain, Italy – they can't get enough shellfish.

"We have some of the best waters in the world for growing it. I would love to see Britain become a nation that eats more shellfish."

It is an ethos that embodies the spirit of what Noble and Lane were seeking to achieve when they founded Loch Fyne Oysters four decades ago.

These days Lane lives in Cornwall with his wife Liz and two sons where, for the past 14 years, he has kept Dexter cattle on Bodmin Moor. He plans to attend Fyne at Forty next weekend.

"I have been back to Loch Fyne periodically, but sometimes you don't want to infest the place," he says. "Time has moved on. New people are running it. Best to keep out the way.

"The last time I was up, I was sitting there looking at the organisation involved now and did slightly break out into a cold sweat. Thank goodness I don't have to do that.

"At its core they are still growing shellfish which is a great life and a positive thing. I am really looking forward to going back."

Fyne at Forty takes place on May 11-13. Visit lochfyne.com