Rinse the salmon slices thoroughly under running water and then pat dry. Rub with salt and pepper. Let the butter melt slowly. Peel the onion, chop it finely and fry it in the butter without letting it turn color. Add the chopped herbs and pour the fish stock and white wine on top. Add capers and bring to the boil. Stir in the creme fraiche and season with salt, pepper and orange juice. Place the salmon slices in the sauce, cover and let stand for 3 - 5 minutes. The sauce must not boil. Arrange the salmon slices on a platter. Peel the orange, cut into thin slices and garnish the salmon with it.