This entire curing process takes about 10 days. Before you begin, freeze the fish for at least 48 hours to kill any parasites and then prepare your ingredients.
Once the fish has thawed, cut the skinned fillets into small 1-inch pieces.
To make the brine, place the diced fish in a glass bowl and add 5/8 cup of plain, non-iodized salt. Cover with 2 cups white vinegar and stir. Refrigerate for 5 days, stirring each day.
After sitting in brine for 5 days, the fish is ready to be pickled. Rinse the fish in cold water twice, allowing it to stand each time for 30 minutes. Drain the water.
Slice an onion and bell pepper into strips and set aside.
Combine 1 ¼ cup vinegar with 7/8 cup granulated sugar and 4 teaspoons of pickling spice. Bring to the boil and then allow to cool completely.
Pack the fish and vegetables into a jar layer by layer, starting with a thick layer of fish. Add a layer of sliced onions and peppers and continue until all of the fish is in the jar.
Pour the cold pickling solution over the fish (covering the fish completely) and refrigerate for at least another 5 days. The fish will be ready after 5 days, but it will be even better if you can resist it for a little longer.