The Big Ingredient: cod

Our appetite for it may have reduced ocean stocks to dangerous levels, writes Christopher Hirst. But new rearing techniques mean it will remain on the menu

The hero, Gadus morhua, is not a nice guy," writes Mark Kurlansky in Cod: A Biography. "The cod is omnivorous - it swims with its mouth open and will swallow whatever will fit - including young cod." If unthreatened, it grows to a vast size. Codfish the size of men have often been reported. One verified monster measured 6ft and weighed 15 stones (95kg). It has the whitest flesh of all fish, containing next to no fat (0.3 per cent) and 18 per cent protein, an unusually high level for fish. Like the pig, almost everything about the cod can be used, the head providing especially tasty meat. The fish dries exceptionally well, when the protein level rises to as much as 80 per cent.

It was dried cod, known as stockfish, that fuelled the Vikings and the Norse discovery of North America. Cod was the major source of protein in Scandinavia. The Norwegians are particularly obsessed with the fish, in both fresh and dried forms. In his magisterial work North Atlantic Seafood, Alan Davidson devotes a page to an account of plain simmered cod steaks. It was cooked for him in Bergen using a freshly killed fish: "I have never eaten cod so good."

In Denmark, small pieces of cod are added to fruit soup. In Sweden, the fish is simmered with butter, dill and parsley. In Russia, it is served with a cherry and red-wine sauce. In Iceland, whose territorial waters contain the world's richest cod fishing grounds, they prefer haddock to cod, a view shared by fish and chip fans in Yorkshire.

Since cod has sadly become a rarer and more expensive fish, we have come to recognise its fine qualities. In any fish cookbook, there are a host of recipes for this versatile seafood. The big-flaked cod roasts superbly. Gordon Ramsay advocates baked cod with lentils and leeks in a mustard dressing or in a butter-herb crust. Sophie Grigson recommends roast cod with a crust of breadcrumbs, lemon, garlic and parsley. She also says that a cod soup with vegetables and cream was "something of a saving grace" when she spent 10 days in northern Norway.

The concentrated flavour of salt cod is a particular favourite of chefs. Rick Stein uses it in a cassoulet with Toulouse sausages and in a stew with chickpeas and parsley. Mitchell Tonks insists that salt cod grilled with oil and wine vinegar tastes "like the best fish and chips that I have ever had" and raves about a salt cod lasagne with onions, mozzarella and parsley: "A cracking family supper." He suggests that you are better off salting your own cod since much of that sold in the UK is too hard.Whether we yearn for it in the form of fish and chips or brandade de morue, our cod is under threat.

As Kurlansky points out: "If ever there was a fish made to endure, it is the Atlantic cod - the common fish. But it has among its predators man, an open-mouthed species greedier than cod." This greed has resulted in the fishing-out of Newfoundland's Grand Banks, once the richest cod fishery in the world. In 1994, Canada's Atlantic cod fisheries were closed, involving the loss of more than 30,000 jobs. After sustaining a voracious fishing industry for 500 years, Canadian cod was commercially extinct.

This warning inherent in this decline is particularly relevant to the UK, since we consume more cod than any other nation on Earth. According to the Marine Conservation Council, North Sea cod is "on the brink of collapse". Though the fish lives to 50 years of age, almost half the cod aged between two and eight is removed from the North Sea each year by fishing.

However, only one-fifth of Britain's cod comes from this area. To conserve stocks, you should try to make sure that any cod you buy comes from Icelandic waters, which are relatively well-stocked. Pollack and saith are similar fish to cod, but their stocks are under much less pressure.

The picture for cod is not entirely black. Production levels of up to 40,000 tons of cod per year from fish farms in Norwegian waters have been predicted within the next decade. Stein insists that fish should not be boycotted because of overfishing worries: "It could force the price down to lack of demand, ending in more of each species being caught to pay fishermen's bills. Go for other species. We must eat fish. It's an essential part of our diet."