1. Place fillets in a pan or a platter. Sprinkle tops of fillets with salt. Refrigerate.
2. After half an hour, rinse the fillets.
3. Place water, sugar, onion, 1/2 teaspoon salt, and pepper in a large pot to boil.
4. Lower flame to medium and add fish. Cook, covered, for 25 minutes.
5. Add bay leaves and dash of vinegar. Cook additional five minutes.
6. Put pot in refrigerator to cool before transferring to container.