2 large onions, thinly sliced
1 tsp whole allspice
2 bay leaves
1 cinnamon stick
1 tsp whole cloves
1 tsp mustard seeds
1 tbsp salt
125驳/4陆辞锄 sugar
250ml/9fl oz white vinegar
1kg/2lb 4oz mackerel fillets, cleaned and cut into bite-sized pieces