Cod, a mainstay food from Britain to Brazil, all but disappeared from Canadian waters in the 1990s after years of overfishing, and scientists say a similar fate awaits the shoals of the North Sea.
But fish farms are putting cod back in North Sea water, at least within enclosed sea pens, easing the strain on wild fisheries and, fish farmers say, protecting a species that would otherwise be fished into extinction.
Off the Shetland Islands in northeast Scotland, Johnson Sustainable Seafoods is providing what it says is a model of good farming practice.
Given more space to roam around their pens and fed a natural diet, the Shetland cod farm has won the backing of Britain's Organic Food Federation.
"Fish farming can be the saviour," said Karol Rzepkowski, managing director of the company. "It takes a little bit of left-field thinking, having the right ethic and the right ethos, and it can be done right," Rzepkowski said.
RESTOCKING THE WATERS?
The Shetland farm expects to harvest 2,500 tonnes of cod this year and aims to double its output in 2008. Other producers include Pan Fish in Norway, which recently acquired Marine Harvest to become the world's leading fish farming group.
Much more is needed, though, if cod farming is help redress the decline in the wild population. Globally, the wild catch has plunged to about 1 million tonnes a year from 4 million in the 1960s. Stocks in northern waters, especially the Barents Sea, remain strong, but the World Wildlife Federation and others warn that overfishing is changing that.
Experts say it will be a long time before farmed cod production rivals the wild catch. "I don't think at this stage we are anywhere close to that," said Barrie Deas, chief executive of the Britain's National Federation of Fishermen's Organisations (NFFO).
Farmed cod will also be hard pressed to match the popularity of farmed salmon, more than one million tonnes of which were consumed last year, say aquaculture analysts at Norway's Kontali Analyse.
Salmon is better suited to aquaculture and its distinctive pink hue offers a marketing advantage over cod's white anonymity, Kontali Analyse noted.
For now, attracting more attention than production figures is Johnson's claim that it is raising the world's first organic, sustainable cod.
One staunch opponent of the aquaculture industry is Bruce Sandison, chairman of the Salmon Farm Protest Group, based in Scotland. Barely pausing for breath, he reels off a list of problems: diseases have spread in crowded sea pens; farmed fish have escaped and damaged wild stocks; the farmed product is less healthful for consumers.
"The same thing is going to happen with cod," he said, pointing out that a disease called Francisella decimated about half the cod in a Norwegian fish farm in 2005.
"What we're playing with here is a wild species that has existed on the planet since probably the end of the last ice age. We're pushing that towards extinction, and we're going to replace it with a totally artificial species."
Questions have also been raised about the sustainability of fish farming. It takes a huge cull of smaller wild fish, about four tonnes worth, to feed every single tonne of the captive population.
The Shetland farm has found a way around this problem. All its cod are fed with the "off-cuts" -- scraps destined to be discarded -- of wild fish already caught for human consumption.
"I doubt if that would be practical if the kind of expansion that is envisaged takes place," said Deas of Britain's National Federation of Fishermen's Organisations.
Aware of this limitation, researchers are beginning to consider alternative food sources, raising a distant prospect of truly sustainable fish farming. And if organic farms are also successful in curtailing harm to the broader environment, aquaculture could win over more of its critics.
"There would not be a lot left for us to moan about," said Tom Pickerell, a fisheries policy officer at the World Wildlife Fund-UK.
FROM SEA PEN TO TABLE
In the meantime, Johnson's Shetland cod has been able to lure a growing number of customers. Sold under the No Catch brand name, it is available in hundreds of Tesco and Sainsbury's supermarkets across Britain.
"It allows people to enjoy cod but without having any sort of guilty conscience about where that cod is coming from," said Joanna Keohane, spokeswoman for Tesco.
The avoidance of guilt is clearly a powerful influence in some markets: British shoppers are happy to pay a premium for the farmed cod over its wild brethren.
