Bluefish and Fennel in Papillotes

This recipe comes from the Cotentin peninsula of Normandy, where it is made with mackerel fillets, which could replace the bluefish if not available. Because of this preparation, gooseberries in Normandy have been given the name groseilles a macquereau or mackerel berries. You can replace them with red or black currants or any acid berry such as wild cranberries, regular cranberries, white raspberries, cloudberries, or salmonberries.