For those of you that want to cold smoke trout or salmon, here is how I do it.
I use 3 parts brown sugar to about one part salt, maybe a little less. Normally I cut the fillet into smaller 3" square pieces so the brine penetrates the pieces. I always leave the skin on. Layer the fish into a plastic container and pack the mixed dry brine in. I usually try and stir it up every 12hrs or so, and a lot of liquid will get sucked out of the fish. I have done a brine as short as 24hrs and as long as 4 days. After its brined, take the pieces out and rinse them with cold water, placing them on a rack. I have a couple of muffin fans that I use to form the pellicle. This is probably the most important part of cold smoking salmon, is forming the pellicle. You want to dry the fish out until it is tacky. What this does is it seals in the moisture and allows the smoke to do its magic. I use a little chief smoker and a couple of pans of chips is all it takes. I leave the fish in there until it is dried to the consistency that I am looking for.
Trust me I ruined a whole lot of salmon before doing it this way and I have yet to get a bad batch. If you want to you can also sprinkle any kind of dried spices on the fish while the pellicle forms. It will get glued onto the fish and it does add some zing. I like to use course ground black pepper or some dried habanero powder if I want to add some heat. If I was going to smoke any fish this is how I would do it honestly.