Read more about preparing fish for smoking in Mike Stines' article here.
Use only fresh fish that has been kept clean and cold. Salmon are split with the backbone removed or filleted; bottom fish filleted; herring and smelts are headed and gutted. (Herring are also traditionally split for kippers.) Rinse the fish with running cold water to remove all traces of blood.
4 cups cold water
1/4 cup (2.5 ounces or 70 grams) kosher salt
1/4 cup dark brown sugar, packed
2 bay leaves
1 stalk celery, sliced
1/2 cup chopped yellow onion
2 cloves garlic, smashed
Bring two cups of water to a simmer over medium heat. Add the remaining ingredients and stir until the salt and sugar dissolve. Remove from the heat and add the remaining cold water. Cool the brine to 40 degrees F. (Use one gallon of brine for every four pounds of fish.)
If you don’t want to make your own brining solution or want a variety of flavored brines, Hi Mountain offers several brine mixes including a trout brine, gourmet fish brine and Alaskan salmon brine.
Place the fish in a non-reactive container and add the brine. Cover and refrigerate.
Brine 1/2-inch thick fillets for two hours, one-inch thick pieces about six hours, and 11/2-inch thick pieces overnight. Brining times can be adjusted to give the fish a lighter or heavier cure. Brining pickles the fish so the longer it brines the saltier it will get.
Another option is to dry cure the fish instead of using a brining solution. See recipe for dry cure here.