When smoked salmon will be used as a substitute the butter amount will be too much because smoked salmon is already more oily then the cod or haddock, so do cut down on the butter.
This is a very tasty blend of ingredients! I found this to be extremely fast easy to put together as well as an excellent use of little bits of ingredients you might have left over - the cooked rice, boiled eggs, etc. I think you could certainly use any sort of leftover flaked, meaty fish if you didn't happen to have any haddock or cod. I used a verygood quality smoked salmon that tasted heavenly in this. The only drawback I found was the huge amount of butter - which made it too greasy. Next time, I would use half the butter called for in this, as the butter flavor was a bit too pronounced and it was oily. Also - I tried this two ways, one with the spicy ingredients, and a mild version for my child. Either way it was very tasty, but I preferred it with a bit of heat.