Put fish fillets and salt in ice cream pail and cover with vinegar. Cover. Refrigerate. Keep in refrigerator 5 or 6 days, stirring every day. After 5 or 6 days, rinse fish in cold water. Let stand in cold water for 1 hour. Drain well. Layer fish in jars with raw onions. To each pint jar add: 2 bay leaves, 1/2 tsp. whole peppercorns, 1/2 tsp whole allspice, 1/2 tsp. mustard seeds. For brine, boil and cool: 5 c. vinegar, 2 c. water, 2-1/2 c. sugar. Pour cooled mixture over fish and spices in jars. Ready to eat in 4 to 5 days. Keep refrigerated. Keeps many months in refrigerator.