Conservationists have expressed dismay at the rapid growth in European cod farming following new figures released last week.

Norway, which accounts for around 80% of the world's farmed cod production, increased its national production by 59% from 10,375 tonnes in 2007 to 16,523 tonnes in 2008. The figures, from the country's Directorate of Fisheries confirm the rapid growth in the cod farming industry, but they have prompted fears from green groups that the expansion will lead to more escapes from farms and contamination of the gene pool of wild populations.

"We are very concerned at the current levels of cod farming," said Nina Jensen, head of conservation at WWF Norway. "No environmental impact studies of cod farms have been done, there are no restrictions on location, there are no restrictions on the protection of spawning grounds and there are lots of fish that escape."

Around 228,000 cod escaped from Norwegian farms last year, compared with around 100,000-odd salmon – even though the salmon farming industry is 60 times bigger than cod farming. Cod are more exploratory by nature and so are better at finding their way out of nets. When they escape, farmed cod may breed with their wild cousins and pass on disease.

"Farmed fish are more prone to diseases and parasites than wild fish. So when cod escape from the farms, they could infect the wild populations," said Dr Geir Lasse Taranger, a scientist at the Norwegian Institute of Marine Research.

Interbreeding could also reduce the wild gene pool. "We need genetic variety to ensure the long-term survival of the species and we are losing genetic variety all the time," he said. "The growth in the cod industry should be chilled down until all the problems are sorted."

The new figures confirm the booming growth of the commercial cod farming. In Norway alone, it went from 248 tonnes in 2002 to 1,685 tonnes in 2004 and 5,519 tonnes in 2005 – overall, an increase of more than 6500% in seven years. Current world production, which takes place also in the US, Canada, Iceland and Denmark, is estimated at about 20,000 tonnes.

Defenders of cod farming, however, say the industry is one way to meet the growing demand for fish at a time when wild stocks are in decline around the world. "Cod farming is definitely part of the solution," said Henrik Vikjær Andersen, market director of Codfarmers, one of the world's largest cod farming companies, based in Norway. "We have exhausted pretty much all the possibilities for food production on land, so the opportunities to increase protein production definitely come from the sea and from aquaculture."

"We provide stability and regularity because we can deliver 365 days a year, unlike wild cod, which depends on catches," he said. "It is also ultra-fresh because it is packed no more than four hours after it was taken out from the sea."

Despite its phenomenal growth, cod farming is still a modest industry – the Norwegian salmon farming produced 742,000 tonnes of fish in 2008. And there have been many hiccups along the way. Last year Shetland's Johnson Seafarms, the world's first organic cod farm, went into administration with debts of £40m, partly because the production costs were too high. Codfarmers has yet to make a profit and a major player in aquaculture, Marine Harvest, pulled out recently of cod farming.

One problem is the decrease in the price of wild cod, which makes farmed cod less attractive. It has also proved difficult to develop a cod breed resistant enough to lice and disease or the fact that a high proportion of the cod cannot be grown to a big enough size to be sold.

Despite these problems, the industry hopes that cod farming can in future become as big as salmon farming is today. "Twenty years ago I heard a researcher say that the Norwegian salmon industry could never produce more than 10,000 tonnes," said Andersen. "And now we are at more than 700,000 tonnes." In the next two to three years, Norway alone is hoping to increase its production to between 15,000 and 30,000 tonnes.