I like to boil mine up to soften the bones (if any) and they like it warm on these chilly winter days.
I don't know that they're equipped to eat it raw like eagles do... g
The light tuna should be fine... the albacore tuna seems to have more residual mercury, and it is recommended to only consume 1 can per week, especially for expectant mothers. Once in a while as a treat to the chickens won't hurt them. We always seem to wind up with extra salmon and halibut...