The "Club Med" of southern European Union countries came under attack from environmentalists today for defying the campaign to ban trade in bluefin tuna, Japan's highly prized sushi fish, whose stocks are dwindling dangerously low.

A fortnight ago the European commission agreed, after weeks of argument, to back a proposal from Monaco to ban trade in bluefin tuna. If the EU had voted for the ban at an international forum next March, fishing for bluefin tuna would have been effectively outlawed, at least temporarily.

Despite optimism that the ban, supported by 21 EU governments, would go ahead, the move was blocked at a Brussels meeting late yesterday by Malta, Cyprus, Spain, Italy, France, and Greece.

"Deplorable," said Xavier Pastor, head of the Oceana fisheries conservation lobby group in Europe. "They are pushing tuna to the point of no return."

"Enough is enough," said Aaron McLoughlin, head of the WWF European marine programme. "It is once again large-scale Mediterranean fishing interests trying to gang up against the long-term survival of Atlantic bluefin tuna."

French opposition was a particular surprise as President Nicolas Sarkozy made a speech in Brittany in July calling for the tuna ban, which is backed by Britain, Germany and most EU states who support Monaco, the first country to ban trading in bluefin tuna because it is endangered.

Stocks of the fish in the Mediterranean have hit almost extinction level, according to experts, with bluefin tuna thought to be below 18% of the total in 1970.

"As a result of both legal and illegal catches, over the past decades the species has experienced a sharp decline and its conservation status is now very poor," the European commission has said.

• This article was amended on Wednesday 23 September 2009. We mistakenly listed Portugal among the countries who opposed the ban on trade in bluefin tuna, and omitted Greece. This has been corrected.