Fish
Haddock
Melanogrammus aeglefinus · also called haddocks
A haddock carries a dark mark above each pectoral fin so distinctive that legend attached it to a story about Saint Peter pulling one from the Sea of Galilee — fishermen still call it the devil’s thumbprint. That same small mark is also the easiest way to tell this major North Atlantic food fish apart from its close relative, cod.
Overview
The haddock, Melanogrammus aeglefinus, is a bottom-dwelling North Atlantic groundfish found over sand, gravel, and mud on the continental shelf. It feeds on worms, molluscs, and crustaceans along the sea floor, and is easily distinguished from cod by a dark lateral line and the distinctive shoulder blotch above each pectoral fin.
A fishery with a recovery story
One of the most commercially important groundfish species, haddock stocks suffered serious 20th-century overfishing, particularly in the western Atlantic. Sustained quota systems and catch limits have since helped several previously depleted stocks recover meaningfully.
Status
Least Concern, with major North Atlantic stocks now stable or recovering under active fishery management, though regional health still depends on continued careful monitoring.
Haddock: common questions
What is the dark mark on a haddock's side actually called?
The distinctive dark, roughly circular blotch located just above and behind each of a haddock's pectoral fins is commonly nicknamed the devil's thumbprint in some regions, while other traditions call it St. Peter's mark, referencing a legend that the apostle Peter left the mark with his fingers when he caught a haddock in the Sea of Galilee. Regardless of the name used, the mark is a genuinely reliable and easily visible feature that helps distinguish haddock from other similar-looking North Atlantic groundfish, particularly cod.
How can you tell a haddock apart from a cod?
While haddock and cod are closely related and broadly similar in overall body shape, haddock can be distinguished by a darker back, a distinct black lateral line running the length of the body, and, most reliably, the dark blotch above each pectoral fin that cod entirely lack. Cod, by contrast, typically has a more mottled, brownish or greenish pattern and a pale lateral line rather than a dark one, differences that fish sellers, chefs, and anglers commonly use to tell the two commercially important species apart at a glance.
Has haddock fishing always been sustainable?
No, haddock stocks in parts of the North Atlantic, particularly in western Atlantic waters, experienced serious depletion during periods of intensive, poorly regulated fishing pressure in the 20th century, which prompted the introduction of stricter fishery management measures including catch quotas and closed areas. Under this sustained management, several previously depleted haddock stocks have shown meaningful recovery, though the health of any given regional stock still depends heavily on continued, carefully monitored fishing pressure and favourable environmental conditions.
Where does haddock typically live and feed?
Haddock is a bottom-dwelling, or demersal, species generally found over sand, gravel, or mud seabed on the continental shelf of the North Atlantic, at moderate depths where it forages primarily for small invertebrates such as worms, molluscs, and crustaceans living on or just under the sea floor. It generally prefers somewhat cooler water than many other commercially important groundfish and shows some seasonal movement within its range in response to changing water temperature and the availability of food.