Scottish fishermen have resorted to sailing to Denmark to land their catch as Brexit red tape continues to delay exports, an industry body has said.
The Scottish Fishermen's Federation, which campaigned to leave the EU, also said the Brexit trade deal was the worst of both worlds for the industry.
Many fishermen "now fear for their future", it said.
The UK government said the deal would "bring immediate gains to our fishermen and women across the whole UK".
Late last year, the Scottish Fishermen's Federation (SFF) said it was "deeply aggrieved" by the Brexit deal.
Fishing firms have also warned of impending bankruptcy as delays continue at ports following the introduction of post-Brexit regulations.
'Desperately poor deal'
On Friday, the SFF kept up the pressure on the UK government.
In a letter to Prime Minister Boris Johnson, it said some fishermen "are now making a 72-hour round trip to land fish in Denmark, as the only way to guarantee that their catch will make a fair price and actually find its way to market while still fresh enough to meet customer demands".
Quotas are used by many countries to manage shared fish stocks. They determine how many fish of each species each country's fleets are allowed to catch.
The SFF said that Brexit quota gains "can hardly be claimed as a resounding success" and that the Brexit deal "actually leaves the Scottish industry in a worse position on more than half of the key stocks".
"This industry now finds itself in the worst of both worlds," said SFF chief executive Elspeth Macdonald, accusing Prime Minister Boris Johnson of broken promises on quotas.
The "desperately poor deal" reached on quotas, under which the EU "have full access to our waters" means that the UK has "no ability to leverage more fish from the EU", she said.
"This, coupled with the chaos experienced since 1 January in getting fish to market, means that many in our industry now fear for their future, rather than look forward to it with optimism and ambition," Ms Macdonald added.
'Extreme Brexit obsession'
The Scottish National Party said the letter was "an utterly devastating verdict on Brexit from Scotland's fishing industry".
An SNP spokesperson said the Scottish fishing industry was "right to be angry" about the Brexit deal, which it said was costing Scotland's fishing communities millions of pounds.
The spokesman called on the prime minister to deliver "a multi-billion pound package of Brexit compensation for Scotland", adding: "Communities across Scotland will never forgive the Tories for the damage they are doing to our country with their extreme Brexit obsession."
A UK government spokesperson said the Prime Minister would respond to the SFF letter in due course.
The spokesperson said: "We have now taken back control of our waters and the agreement we have reached with the EU secures a 25% transfer of quota from EU to UK vessels over five years, starting with 15% this year."
The spokesperson said the government was looking at providing additional financial support for the Scottish fishing industry, which it recognised was facing "some temporary issues".
"The Prime Minister has already committed to investing £100m in the UK's fishing industry and provided the Scottish government with nearly £200m to minimise disruption for businesses," the spokesperson added.