My betta adores salmon! I was a bad girl not long ago and while having some canned salmon, decided to try it out on him.
Took the tiniest piece and put it in the tank. He attacked it right away. Salmon being the consistency that it is, breaks appart. This piece broke into 3 or 4 pieces and some fell to the bottom. He has largish stones as gravel so you can imagine the work it was for him to get at those lost pieces.
My Betta isn't usually driven to eat from the bottom except for that one time his salmon fell there... so he HAD to love the flavor.
I imagine fresh salmon that's been cooked would be better for a betta, as the salt content in the canned can't be the healthiest for them?