Spread softened butter onto bread and cut into 12 2” squares. Gently press buttered side of bread in to parsley to coat. In a small bowl combine onion and radish and mix well. Divide this mixture among the bread squares. Roll each herring fillet into a coil and arrange the herring and capers on top of the bread squares.
The canapés may be made 30 minutes in advance and kept covered and chilled.