The protestors expect to be joined by another 6,000 fishermen from France and Portugal. Earlier in the day, some of the protesters attempted to enter the European Commission building to put forward their demands, but said they were denied access.
The EU's executive body has said it is only ready to engage in talks with official representatives of trade unions, Belgian media reported.
The protesters, who are demanding a nearly 50% cut in marine fuel prices and an extension of cod fishing quotas, threw stones at police and at EU buildings, breaking several windows. Police used water cannons and batons to disperse the crowd, and have detained 74 rioters.
The fuel price protests, which have also involved truckers and taxi drivers from across Europe, started late in May in France, where the price of marine diesel has risen by around 30% since the start of the year.
About 60 truckers and taxi drivers disrupted traffic during a fuel protest on the Paris ring road leaving to the La Defense, where French oil giant Total is headquartered.
Rising fuel prices will be the focus of talks at the EU summit to be held on 19-20 June, among other economic issues such as soaring food costs.
