1. Bring the vinegar, water, sugar and salt to a boil.
2. Let cool completely. Cut the salmon into pieces approximately 1"x2".
3. In a ceramic crock, glass bowl, or plastic container, place a layer of salmon pieces, then a sprinkling of pickling spices and bay leaves, a layer of onions, then repeat the cycle until you have used everything up.
4. Pour the cooled marinade over the fish. Cover and refrigerate at least 3 days.
5. Serve the salmon with its onions, with matzo and butter and sliced cucumbers with sour cream dressing, or if serving with a meat meal, just with matzo.