Hey now...Alder is the best for salmon, hands down. If you can't get your hands on some, Cherry will do just fine.
I would cut the wood 50/50 though..just for that Hickory kick...I like it.
Well I had an old Indian tell me to use crushed corn cobs. Leave a very light smoke flavor. nOt a fish eater But i have used it once for a friend and he was surprised by the flavor.