Haddock

Haddock, North Atlantic fish (Melanogrammus aeglefinus) resembling a cod, distinguished by its 3 dorsal fins and the dark patch just behind the gills, known as St. Peter's thumbmark, which the cod lacks. Haddock live in shoals and feed on worms, shellfish, and other bottom-living animals. They are caught in trawls along with cod, and are important commercially, being marketed salted or as smoked Finnan haddock.