Source: Jewish Holiday Kitchen - Joan Nathan

INGREDIENTS:

One 3½-pound carp, pike, trout, or salmon 
Salt
4 Cups water, or enough to cover fish
½ cup red wine vinegar
1 lemon, sliced and seeded
1 medium onion, sliced in rings
1 bay leaf
1 tsp whole peppercorns
½ cup raisins
1 tbsp salt
5 whole cloves
½ cup brown sugar
4-5 gingersnaps or lebkuchen

DIRECTIONS:

1. Clean, slice, and salt the whole fish, cutting through the bone. Let stand several hours or overnight. 
2. Boil together the water, vinegar, lemon, onion, bay leaf, peppercorns, raisins, 1 tbsp salt, and cloves. Add the fish to the liquid and let simmer un-covered for 10 minutes.
3. Add brown sugar and gingersnaps (the gingersnaps add color to the sauce).
4. Simmer 10-15 minutes more, until the fish is done. The fish should be light and firm to the touch, and the flesh should leave the bones easily.
5. Remove the fish from liquid, skin, and separate the meat from the bones. Arrange on a platter.
6. Boil the liquid 15 minutes longer and let cool. Then strain, removing the onions and raisins from the strainer. Pour the liquid over the fish and garnish with the raisins and onion rings. Refrigerate until the sauce jells. Serve as an appetizer the following day.