Fishermen's leaders from France, Spain and Italy have been meeting in Paris to co-ordinate strikes and protests over the next three weeks in the run-up to a European Union fisheries ministers' meeting.
The protesters are calling for direct immediate aid for the fisheries industry, coupled with increased subsidies.
The European Commission said in a statement it was willing to show flexibility towards the industry but it has ruled out subsidies to offset rising fuel costs.
Short-term aid packages were acceptable as long as they were used to address structural deficiencies in the fleets, it said.
'Ruin for fishermen'
Several thousand fishermen marched on the agriculture ministry in Madrid, where they handed out 20 tonnes of fresh fish to members of the public in an attempt to draw attention to their ailing industry.
Fishermen held protests in Brussels and Madrid
Many blew whistles and klaxons, and let off firecrackers producing red smoke.
The BBC's Steve Kingstone at the protest said he could see flags from Catalonia, the Basque country and Galicia.
One banner read: "Soaring diesel plus cheap fish equals ruin for fishermen." Another chided Prime Minister Jose Luis Rodriguez Zapatero: "You are sending us to the cemetery."
We must mobilise like the French and if we have to block ports, we'll block them
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