If you want to smoke it, yes you have to brine it. Otherwise you are just cooking it. 50/50 canning salt to brown sugar. Mix enough up to cover fish. Cover and refrigerate over night. Rinse real good under cold water. Let fish dry in open air for an hour or two. Smoke using cherry wood keeping the smoker at 180degs or a little less. Get fish internal temperature to 165degs and you will have some smoked fish
Make a rub of 1 cup of Morton’s Tenderkwik and 1 cup brown sugar. Leave the skin on the fillets and rub the rub into the meat side of eat fillet and place in a Tupperware cake pan or put the fish inside a plastic bag and lay them in a metal cake pan in the fridge for 24 hours. Rinse, pat dry with paper towel and smoke. Your fish will be considerably firmer this method over brine.