Fillet the fish and discard the skin. Portion fish fillets to about 150 g and pull the bones. Roughly cut fish bones, head and cooking steps of fish fillets, if any, and rinse under tap water. Put fish bones on with tap water, bring to boiling point and skim off gray foam (if any) with a skimmer (Do not cook on stove, as alternatively stock will become cloudy). Add white wine, greens and spice bag. Allow to simmer for 20-30 min. Then pour the stock through a straining cloth.
The remaining fish stock can be frozen as ice cubes, brewed in preserving jars or possibly vacuum packed and used for many other recipes! Heat the goose fat in a saucepan. Sauté the onion, finely diced, in the fat without coloring. Rinse the sauerkraut under running tap water and add to the onions.
Add pear juice and white wine, bay leaf, juniper berries and clove in the spice bag and cook covered for 150 minutes. Grate peeled pears with a vegetable grater to the cooked sauerkraut. Add whipped cream and cook briefly on the stove. At the end you can add a few pine nuts for refinement.
Reduce fish stock to one third. Add poultry stock, port wine and red wine and boil another third. Bind with stirred tapioca starch. Add the butter.
Season with salt and pepper.