Diners in restaurants in the Belgian capital may be in for a surprise after a report found 30% of fish is being substituted with cheaper alternatives.
The study, by Oceana environmental group, says more than a third of fish is being mislabelled in and around Brussels' European Union institutions.
In EU canteens, where many European officials eat, 38% of fish is wrongly labelled.
Oceana's executive director, Lasse Gustavsson, called it "total chaos".
"The EU needs to clean up its fishy business, take responsibility and urgently improve traceability and labelling of seafood," he said.
The investigation inspected DNA from over 280 samples in 150 restaurants in Brussels' tourist and EU areas. Overall, 31.8% of fish was mislabelled.