In a non-corrosive pot, combine all ingredients except fish. Bring to the boil, reduce, and simmer for 30 minutes. Add fish to simmering brine and poach 12 minutes before removing from the heat.
Let stand to cool 1 hour before placing in a non-corrosive container large enough to hold all the liquid. Cover container and refrigerate fish totally submerged in brine for 3 days.
Serve with black bread, sour cream, and onions.