After the fish has steeped in the hot oil for 30-45 minmutes, take it out and put into a clean plastic or glass container.
Let the oil cool to room temperature, then strain it through a piece of cheesecloth and use it to cover the fish. Make sure you do not include any liquid that the fish gave off during cooking. You want only the oil covering the fish.
Covered this way (use more clean oil if there is not enough), the fish will last in the refrigerator for 2 weeks.
If you want it to last longer, you must pressure-can it in a steam canner. Follow your canner's instructions.