some like to use a dry method, and then there is a brine method. only reason i go with the brine is you dump all ingreds in a non reactive container and mix and dump the fish pieces in.
here is a brine recipie from my grandpa...
smoked fish brine
2 3/4 cups pickling salt
10 qts cold water-use good water
1 cup brown sugar
2 tbls garlic salt
soak avg sized pieces 24 hrs in a refrig or other area between 32-40 deg. soak in fresh water 1 hour
big thick pieces of fish, may require more time and smaller less. once out of brine set on a rack with a fan blowing across fish til outside of fish dry, a coating will form on it called the "pellicle", is now ready for smoker. i also like to rub some brown sugar on the meat.
so when i smoke mine, i generally keep the temps down til i get the color i am looking for. then i will increase temps a bit, 180-200 and leave in smoker untill the medium thickness areas start to flake. the residual heat will continue cooking the thicker portions and they will be done as well. tail sections or thinner pieces may have to be pulled earlier....