I found this for you. It's from the smoker-cooking.com website. I haven't tried this myself.
Smoked Catfish Brine Recipe
To give the fish a good flavor and the right texture, it needs to be brined for a few hours before smoking. To make the catfish brine, combine...
* 1 gallon cold water
* 3/4 cup non-iodized table salt, or canning salt
* 1 cup brown sugar
* 1/2 cup soy sauce
* 3 cloves of garlic, crushed
* 1 tablespoon ground black pepper
* 1 teaspoon ground cayenne pepper
Mix until the salt and sugar are completely dissolved.
Preparing The Catfish
For best results, use fillets that are about the same size and thickness. Thinner fillets take less time to brine and less time to smoke. If you're brining and smoking whole sides, trim off the thin belly edge and the thinnest part of the tail end so the overall thickness is fairly consistent from end to end, and top to bottom.
If you haven't already, remove the skin from the fillets, too.
Use a non-reactive container to brine in. That would include glass, ceramic, crockery, plastic and stainless steel. Heck, you could even use a couple of gallon freezer bags to brine in. Actually, those are about the best.
One gallon of brine is enough for 5 to 6 pounds of fillets. Get 2 freezer bags and place about 3 pounds of cat fillets and 1/2 gallon of the brine in each of 'em.
Place the bags in a large bowl (just in case they spring a leak) and put it in the fridge. Leave it there for 4 hours. Move the brining catfish around a few times while it's in the fridge so it brines evenly.
Time's Up! Remove the catfish from the bags and give the fillets a quick rinse. Pat dry with clean towels.
Lay the fillets on a raised rack, so air can reach both sides. Let the fish air dry for an hour or so at room temperature, until it's not sticky anymore. It should start to get a slightly hard coating on the surface. When it does, it's ready to smoke.
How To Smoke Catfish
You can make smoked catfish in a regular smoker or in a grill.(see Gas Grill Smoking) It's important to keep the temperature down just below 200 degrees if you can. 190 is good. If the smoker temperature gets too hot, the juices will start to bleed out of the fish, and it won't be as moist.
Apple or cherry is good wood to use. It won't take a whole lot, either. One good fist sized chunk, or a couple handfuls of water soaked chips wrapped in foil should do it. And if it's not smokey enough for you, use more the next time.
Continue smoking the catfish until it flakes. Remove it an let it thoroughly cool before eating. Your smoked catfish will keep stored in the fridge for up to a week. If it's going to be kept longer (hidden, that is) wrap it tightly in plastic wrap, then in foil and freeze it. It will keep 6 months in the freezer.
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