Cut the herring fillets into 2-3 cm long pieces.
Peel two oranges, quarter them and cut them into thick wedges. Peel the mango and cut the flesh into cubes from the core. Set aside some fruit for garnish. Mix the remaining fruit pieces with the herring pieces.
For the marinade, first pluck the dill flags, taking off about 2 tablespoons for the garnish. Squeeze the orange. Mix the orange juice with sugar, pepper, salt, horseradish and crème fraîche. Mix in the whipped cream and finally stir in the dill.
Mix the fruit and fish mixture with the marinade and let it infuse well. Garnish the herring salad with the remaining fruit and the dill flags before serving.