Have your fish store grind the fillets or grind them yourself in a food processor or meat grinder. Do not puree, but grind fine. 

 Saute the diced onions in the oil until soft and transparent but not brown. Cool. 

 In the bowl of an electric mixer fitted with the paddle attachment, place the fish, onions, eggs, matzah meal, salt, pepper, sugar, and 2 cups cold water. Beat at medium speed for 15 minutes. Stir in the dill and grate in the carrots and mix well. 

 Pour the mixture into a greased 12-cup Bundt pan. Smooth the top with a spatula and bake in a preheated 325°F oven for 1 hour in a larger pan filled with 2 inches water. 

 Cover with aluminum foil and continue baking for 1 hour or until the center is solid. Cool for 5 minutes and then invert onto a flat serving plate. 

 Refrigerate for several hours or overnight. Slice as you would a torte and serve as an appetizer, garnished with parsley and served with red horseradish sauce. Leftovers keep for up to five days.