Haddock is a firm fish with lean white meat that is usually thicker and flakes easily when cooked. Because of its similarities with cod, cod can often times be interchangeable with haddock. When substituting cod (or other fish like flounder) for haddock in soup and chowder, adjust the cooking times to avoid over-cooking. Add thicker pieces first and cook for 2 - 3 minutes before adding the thinner pieces of fish. Once all the fish has been added, avoid vigorous stirring.