Fishermen are halting exports to Europe because new border bureaucracy introduced by the government as part of Brexit is making their business unviable.
Exporters now have to deal with new health certificates, customs declarations and other paperwork if they want to sell to the EU, the largest market for much of the UK's catch.
Describing the situation as a "catastrophe", businesses said orders from Europe were also drying up because of Boris Johnson's new trade barriers.
Seafood is highly perishable and relies on a seamless flow across borders, but small test consignments sent to France and Spain that would normally take one day are now taking three or more days, if they get through at all.
It is also taking five hours for firms to secure a health certificate from authorities, a document required to apply for other customs paperwork.
"Our customers are pulling out," Santiago Buesa, director of SB Fish told the Reuters news agency. "We are fresh product and the customers expect to have it fresh, so they're not buying. It's a catastrophe."
Meanwhile David Noble, another exporter who buys from Scottish fleets to export to Europe, told the same agency that the new Brexit bureaucracy was costing between £500-£600 pounds a day and wiping out most of the profit.
"If our fish is too expensive our customers will buy elsewhere," he said.
Donna Fordyce, chief executive at Seafood Scotland, said: "The last 48 hours has really delivered what was expected - new bureaucratic non-tariff barriers, and no one body with the tools to be able to fix the situation.
"It's a perfect storm for Scottish seafood exporters. Weakened by Covid-19, and the closure of the French border before Christmas, the end of the Brexit transition period has unleashed layer upon layer of administrative problems, resulting in queues, border refusals and utter confusion.
“IT problems in France meant consignments were diverted from Boulogne sur Mer to Dunkirk, which was unprepared as it wasn't supposed to be at the export front line. There have also been HMRC IT issues on the UK side that need to resolved ASAP regarding certification.”
She said a lack of knowledge of the required paperwork was also making shipments take far too long and called for checks to be relaxed.
While lorries are physically moving smoothly through Britain's ports without tailbacks, freight volumes have dropped sharply and businesses are simply staying away from the new border on account of the bureaucracy.
Stena, the ferry company that operates many services said it was cancelling a dozen sailings between Wales and Ireland next week because of "a decline in freight volumes during the first week of Brexit".
Speaking on Friday morning, Transport secretary Grant Shapps defended the new barriers to trade, adding there had been some "changes".
"The cabinet office are working very closely with businesses," he said.
"It's not the case that goods have stopped flowing. In fact just before I came on I was studying, as I do by the hour at the moment, the flow at Kent and it's been picking up every single day of this year so far.
"You're seeing goods crossing the short straits and flowing perfectly smoothly - so far not the 11-mile traffic jams we were told about."
Mr Shapps admitted it had been a "quieter start to the year" but said this was on account of stockpiling ahead of a possible no-deal. He said "less than 1 per cent of vehicles" were turning up without paperwork.
"We may well see busy times again but at the moment the border is in fact flowing and it's flowing very smoothly," he told BBC Radio 4.
"I speak to the French ... and they are telling me that they are very keen to keep that border flowing very smoothly, not least because they sell more stuff to us than we sell to them, so it's in their interest."
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