When we run our smokehouse (used for 100+ pounds of DEER/ELK pepperoni), we use the
split alder. ours has propane burners, so we use green alder. You will want to use some fairly seasoned wood, as you will need it to keep the fire going. Maybe a small pile of charcole to get things going then swith to the alder.

Don't use any wood with the bark on it. It will impart a bitter flavor to your fish. Good luck, and have fun.