The haddock or offshore hake is a marine fish distributed on both sides of the North Atlantic. Haddock is a popular food fish, widely fished commercially. The haddock is easily recognised by a black lateral line running along its white side, not to be confused with pollock which has the reverse, ie white line on black side, and a distinctive dark blotch above the pectoral fin, often described as a "thumbprint" or even the "Devil's thumbprint" or "St. Peter's mark". Haddock is most commonly found at depths of 40 to 133 m, but has a range as deep as 300 m. It thrives in temperatures of 2Â° to 10Â°C (36Â° to 50Â°F). Juveniles prefer shallower waters and larger adults deeper water. Generally, adult haddock do not engage in long migratory behavior as do the younger fish, but seasonal movements have been known to occur across all ages. Haddock feed primarily on small invertebrates, although larger members of the species may occasionally consume fish. Growth rates of haddock have changed significantly over the past 30 to 40 years. Presently, growth is more rapid, with haddock reaching their adult size much earlier than previously noted. However, the degree to which these younger fish contribute to reproductive success of the population is unknown. Spawning occurs between January and June, peaking during late March and early April. The most important spawning grounds are in the waters off middle Norway near southwest Iceland, and Georges Bank. An average-sized female produces approximately 850 000 eggs, and larger females are capable of producing up to 3 million eggs each year. Haddock is a very popular food fish, sold fresh, smoked, frozen, dried, or to a small extent canned. Fresh haddock has a fine white flesh and can be cooked in the same ways as cod. Freshness of a haddock filet can be determined by how well it holds together, as a fresh one will be firm; also filets should be translucent, while older filets turn a chalky hue. Young, fresh haddock and cod filets are often sold as scrod in Boston; this refers to the size of the fish which have a variety of sizes, i.e. scrod, markets, and cows. Unlike the related cod, it does not salt well, so it is often preserved by drying and smoking. One form of smoked haddock is Finnan haddie, named for the fishing village of Finnan or Findon, Scotland, where it was originally cold-smoked over peat. Finnan haddie is often served poached in milk for breakfast. The town of Arbroath on the east coast of Scotland produces the Arbroath Smokie. This is a hot-smoked haddock which requires no further cooking before eating. Haddock is also the main ingredient of Norwegian fishballs (fiskeboller). The main nutritional value of haddock is as an excellent source of protein. It also contains a good deal of vitamin B12, pyridoxine, and selenium. The fish also contains a healthy balance of sodium and potassium. Overall the meat is extremely lean.