Peel onions and cut them into rings. Boil up vinegar, red wine, sugar, mustard seeds and bay leaf. Season with salt and pepper, add onion rings. Bring to the boil, simmer for about 2 minutes and let cool off. Rinse maties cold, dab dry and cut into strips. Add fish to the red wine marinade and leave to stand overnight
waiting time approx. 12 1/2 hours