Shellfish farmers selling tonnes of oysters in Europe have said post-Brexit customs and border ideas are "utterly deluded" and could wipe out their businesses.
The threat of dissident republican terrorism at checkpoints, delays to cargoes of delicate seed stock and live produce and the potential for expensive trade tariffs are playing on the minds of firms in Northern Ireland.
Darren Cunningham, who runs Killowen Shellfish on the shores of Carlingford Lough in Co Down, launched a withering attack the Government's ambitious open borders proposals.
He said: "Light touch? I just can't see that working. It just can't be done unless they go and look in the back of every lorry, the way it was in the past.
"And I remember those days. Unless they do that it's a lot of old rubbish.
"Sure, you could have three or four old pallets out the back to say it's one thing and a truck full of something else. And they think they can do all this with a few cameras in the sky?"
Carlingford is regarded as one of the most pristine shellfish producing regions in Ireland. More than 1,000 hectares is farmed.
It is a somewhat disputed territory with both Dublin and London claiming ownership of the lough, similar to the row over rights to the Foyle between Donegal and Derry.
In Northern Ireland last year 3,438 tonnes of shellfish worth about £4.3m was produced.
In the Republic that figure was 26,218 tonnes worth 56m euro. Some 4,450 tonnes of oysters and mussels worth almost 7 million euro are harvested from Carlingford.
Hundreds of people are employed north and south.
Killowen Shellfish sells 30 to 40 tonnes of oysters every year to France and Holland and Mr Cunningham remains totally unconvinced of a solution.
He added: "I think they are completely and utterly deluded.
"But it won't be the British Government or the press making the decisions.
"I can't see any positive outcome of Brexit for the UK in general and it's especially going to hurt us here (in Northern Ireland)."
Brothers John and Mark Doran, of Cahir Linn Oysters, warned expensive oyster seed coming into Ireland and valuable cargo for export is under threat of being wiped out if delayed at ports for as little as a day.
John Doran said: "We are not dealing with tins of beans going across Europe. We are a niche product.
"They're not like cows that are fairly hardy. Picking them, checking, packing - it all causes stress.
"It's like a grenade with the pin out."
The Dorans, in their first year of business, have 7.5 million oysters in beds and hopes of a harvest in 2019 - a nerve wracking coincidence as their timetable runs alongside Brexit.
Mark Doran raised concerns about moving shellfish north-south across the lough and vice versa to avoid predation or disease.
He said: "At the minute we have a paper trail. We tell the authorities what we're going to move - that is as frictionless as it gets.
"There's no definitive line that north is north and south is south. Where is the border? It's a constitutional issue."
All the shellfish farmers who trade into Europe fear that new tariffs could wipe out their business and leave them unable to compete with farmers in the Republic.
Mr Cunningham said some trade levies which could be imposed on exporters in the event of a hard Brexit could add 20-30% to the price of his oysters with businesses in the Republic trading for free.
And he warned about smugglers trying to take advantage of differences in tariffs and taxes once the UK leaves Europe.
He said: "Look at the diesel laundering. The whole British Army could not control it. It's unworkable. It's just a mess."
Mr Cunningham said two possible solutions are a referendum on reuniting Ireland or using the seas around the island of Ireland as a natural customs border.
He added: "But if they put a border post up - in Crossmaglen or Ravensdale or wherever - you know what's going to happen then. It's just a red rag to a bull."