Flounder, Haddock, Cod, and Sole are some of the fishes considered the safest to introduce. They are the most easily digestible and lowest on the allergen list. Just make sure you debone the fish properly. You may poach, bake or steam the fish and then puree as you would any other meat. http://wholesomebabyfood.momtastic.com/introducingfishtobaby.htm#Z4rH3e2tppDX8EBm.99
My kods love cod. I personally don't fancy them.
threadfin, salmon are great for babies