Cod is a bottom-dwelling white fish.
A female can lay 9 million eggs a year when fully mature (about 15 years and about 4 feet / 1 metre long.) The eggs float on the surface of the water. The newborn hatchlings will stay on the surface to avoid the small fish lower down which feed on them. As they grow bigger, they move to the bottom of the ocean to start their life there.
Large Cod will eat small Cod. Cod will eat squid, herring, lobster and crabs.
Today (2004) the average Cod caught is about 3 years old, and weighs 5 to 10 pounds (2 to 4 kg.) Before the depletion of the population that occurred at the end of the 1900s, Cod would live over 20 years, weigh over 100 pounds (45 kg) and be over 4 feet long (1 metre.)
When buying fresh Cod, choose fish with no pink or yellow blotches.
Owing to the rising price of cod, it is becoming less of an everyday fish or more of a fish served Fridays or weekends. Though the volume of cod sold is decreasing, the overall sales amounts are increasing, owing to the raised prices. 
Salt CodCod is less than 1% fat, which makes it easy to preserve by drying. In addition to being dried, it is salted as well, so that the fish can be preserved even longer. Though with modern refrigeration this form of preservation is strictly speaking no longer necessary, Salt Cod has come to be an ingredient all its own in many dishes and is still much in demand. You can also get Cod which is dried, but not salted.
Soak salt Cod in water for at least 24 hours. Discard water. Cod has a flavour that stands up well to strong sauces.
Other white fish, particularly Haddock, Hake or Whiting.
Cod are very prone to having round worms in them -- and scientists are finding that this is more and more likely. The worms can also be in other white fish, but because Cod are more susceptible, the worms are often even called "Cod Worms". The worms can be cream-coloured or brown, and may grow up to 1 1/2 inches long (4 cm). They can burrow into the flesh of the fish. Fish processors often try to look for them, and discard the infected parts, but inevitably they miss some. The worms are not harmful to us once the fish is frozen or cooked. But those who find half a worm in a piece of Cod they are eating are often put off Cod for life, and forever haunted with the thought of what happened to the missing half of the worm.
The Basque and the Norse were catching and salting Cod in the 500s. Atlantic Canada became major fishing ground by the early 1500s; by 1550 more than half the fish eaten in Europe was Cod caught off Atlantic Canada and New England. Cape Cod was discovered in 1602 by Bartholomew Gosnold, which was so teaming with Cod that he said they pestered his ships.
Cod has been the official state fish of Massachusetts since 1974.
Literature & Lore
"Bacalao" is Salt Cod in Spanish.