Dice the carrots, potatoes and onions and cook with the spices in the broth for about 20 minutes.
Clean the fish, cut into small pieces, salt and drizzle with lemon juice. Cut the mushrooms into slices. Add the fish and mushrooms to the broth 10 minutes before the end of the cooking time and only let them steep over a low heat. Add the crabs and carefully mix with the remaining lemon juice and the creme fraiche and season to taste. Care with dill.