If those fish aren't somewhat oily they don't smoke good. They get pretty dry. I know people who have tried to smoke crappie, it turned out more like fish jerky.
I smoke trout, salmon and when they come from cold water (in spring breakup the meat is firm) Sucker, Drum and Carp, Bullheads are good smoked. they are oily fish which keeps them moist after smoking.
Brine is simple, add salt to cold water until an egg floats. Leave the scales and skin on the fish, cut the heads off inside the gills and split them down the back bone. Place in a single layer of fish in a large pan (don't stack them on top of each other) and completly cover with the brine for at least 24hrs. I make a glaze of water and brown sugar, and brush that on the meat side when about half done.
You when they get dry, brush on some more glaze. You may need to do that 3-4 times.
A couple things about smoking fish.
1. You need to keep and eye on them. Depending on temp and ambient temp smoking time varies some from batch to batch. You can tell how it going by how firm the meat is. you want it just a little bit spongy.
2. Dont smoke fish in the same smoker as you smoke your other meats in. the meat may have a slight fish taste.
A old refrigerator, preferably all metal no plastic makes a dandy fish smoker.