Due to drastic overfishing and their habit of living in deeper water in the summer (the opposite of many fish), adult cod are not often seen by divers. Other members of the cod family such as bib, ling (pictured), poor-cod, pollack and saithe are encountered more frequently. Family features include a chin barbel and three dorsal fins, but these are not universal. Ling lack the triple fin; pollack and saithe do without a chin barbel.

In areas subject to the heaviest exploitation, such as the North Sea, nearly half of the cod between two and eight years old are taken by fishing every year. This leaves the population on the brink of collapse. For ideas on how consumers can reduce damage to fisheries, see the Marine Conservation Societys Good Fish Guide.

Cod seem to eat virtually anything that moves and quite a lot that doesn't. They prey on a wide range of fish and will track the migratory movement of species such as herring. Squid, crabs, molluscs and worms are also eaten. More unlikely items found in cod stomachs include partridges, keys, books, candles and turnips.

The haddock, and its relative the cod, can communicate by making noises with the muscles of their swimbladder. The grunting and croaking sounds produced appear to be used mainly in courtship. At breeding time, male cod attempt to impress females with a twisting and turning dance routine.

On mating, cod shed their eggs (up to 6 million at a time) and sperm into the sea and leave their parenting at that! Many eggs fail to be fertilised or are eaten before they can hatch two weeks later. The hatchling cod spend a few months near the surface before moving toward the seabed, and it then takes anything between two and 15 years (depending on the population) for the young fish to start breeding.

Cod can measure up to 1.5m and weigh more than 40kg. As a major source of protein-rich food, they have played an important part in history. Cod-liver oil was found to cure rickets and even the skin was used to make glue. The valuable cod stocks off Newfoundland were called silver mines and have contributed to much international strife. These have now been virtually exhausted.