Heat some oil in a pot, add the onions and cook until soft. Add the tomato paste and continue to cook. Add the sauerkraut, fish stock, a pinch of sugar, a pinch of salt and the bay leaves. Cover and simmer for approximately 40 minutes over low heat. Meanwhile, preheat the oven to 220 degrees Celsius. Sprinkle a little salt over the catfish and slice into four thick pieces. Wrap each piece with bacon slices. Place the pieces on a baking sheet and bake in the hot oven at for about 15 minutes. Add some dill to taste before serving.