I feed my dog fish about 2 times a week. Usually sardines or salmon. Either canned or cooked. I NEVER feed my dog raw fresh fish as fish can carry lots of parasites. If the fish has been frozen for a certain amount of time I will allow him to eat it raw as being frozen for a period of time kills the parasites.
Fish is a good, low-fat source of protein, and has lots of Omega-3's which makes for great skin and a good coat.
My dogs eat canned fish, bones and all. Cooked fish is always deboned as the bones may get caught in the throat.