Can I still eat this fish?
I agree with yossarian, if I question it, I chuck it.  Although in this case, the salmon probably will not harm you, it might just taste bad.  Loss of moisture (freezer burn), taking on of flavours, etc.  I wouldn't eat it because it wouldn't taste great.   My father-in-law would eat it, because you don't throw out food (his rule).  Bottom line, if it has been in the freezer for those two years straight, it won't give you food poisoning or harm you.  It's just a matter of palate.  But rest assured, it won't taste great.