Cod

Lore & Background

Gadus morhua was named by Linnaeus in 1758. G. morhua callarias, a low-salinity, nonmigratory race restricted to parts of the Baltic, was originally described as Gadus callarias by Linnaeus. Three species in the genus Gadus are currently called cod.

The fourth species, Gadus chalcogrammus, is commonly called Alaska pollock or walleye pollock, with alternative trade names like snow cod or bigeye cod. Many other fish no longer classified in Gadus have common names ending in 'cod', including members of Gadidae and related families. Some fish commonly known as cod are unrelated to Gadus, partly due to market-driven naming after Atlantic cod stocks shrank.

Reader's Guide

Cods of the genus Gadus have three rounded dorsal fins and two anal fins. The pelvic fins are small, with the first ray extended, and are set under the gill cover (the throat region), in front of the pectoral fins. The upper jaw extends over the lower jaw, which has a well-developed chin barbel. The eyes are medium-sized, about the length of the chin barbel.

Cod have a distinct white lateral line from the gill slit above the pectoral fin to the base of the caudal fin. The back is greenish to sandy brown with mottling, and the belly is white. Atlantic cod can change colour and has two colour phases: gray-green and reddish brown. Its average weight is 5–12 kg, with specimens up to 100 kg.

Pacific cod are smaller and darker. Atlantic cod live in the North Atlantic; Pacific cod in the northern Pacific. Atlantic cod occupy varied habitats, favouring rough ground inshore, at depths between 6 and 60 m (average 80 m), occasionally to 600 m.

They are gregarious and form schools, especially during spawning. Spawning occurs between January and April (peak March–April) at about 200 m depth at 4–6°C. Eggs are planktonic, hatching in 8–23 days. Larvae reach 4 mm, then a planktonic phase of about ten weeks allows growth to about 2 cm. Young cod then move to the seabed and eat small benthic crustaceans.

They reach 8 cm in six months, 14–18 cm by one year, and 25–35 cm by two years. Maturity occurs at about 50 cm at 3–4 years. Adult cod feed on sand eels, whiting, haddock, small cod, squid, crabs, lobsters, mussels, worms, mackerel, and molluscs. In the Baltic Sea, the most important prey species are herring and sprat.