US experts held a second day of hearings into whether to allow genetically modified salmon to become the first so-called "Frankenfood" animal to be served up on American dinner tables.

The meeting, which tackled the thorny issue of labelling, came after a 14-member committee of independent experts consulted by the Food and Drug Administration called for further studies before any decision is reached.

Under the current laws, GM modified salmon would not have to be labelled as transgenic food as it would be exactly the same as other salmon.

The Massachusetts-based AquaBounty argues that its fish, injected with a gene from the Pacific Chinook salmon, can reach adult size in 16 to 18 months instead of 30 months for normal Atlantic salmon.

But it has said that in all other respects, its AquAdvantage salmon "are identical to other Atlantic salmon."

If GMO salmon is given the green light, consumer groups are demanding that the FDA require it to carry a GM label, even though supporters of the new salmon argue that such a label might lead consumers to shun the fish.

Michael Hansen, from the Consumer Union, argued that it was too early to tell if there would be any ill effects for consumers.

"It's essential to label the GE (genetically engineered) animal so that any effects will be recognized and consumer health protected," he said.

"Recently certain drugs approved by FDA as safe have turned out to have unexpected health effects after they were widely used by consumers."

The "FDA should require labelling to ensure that any unexpected or unintended effects of engineering this salmon ... come to FDA attention," he added.

AquaBounty has insisted it would only rear GM salmon in inland hatcheries, and that only sterile female salmon will be sold to farmers.

The new strain could help meet rising demand for fish and reduce pressure on wild fish stocks, the firm contends.

AquaBounty has tried for several years to win a green light from the FDA to breed and market its GM salmon. The company has said it would take two to three years from FDA approval before its salmon would hit store shelves.

But a coalition of 31 groups is urging the FDA to reject the application, with critics warning the new salmon could exacerbate the problem of farmed fish escaping from tanks and breeding with wild counterparts.

According to a recent poll 95 percent of Americans are in favor of labeling such genetically modified foods.

"Americans want a choice, and labelling is imperative in order for consumers to have the choice," said Anna Zivian, from the environmental group Ocean Conservancy.

But others argued that if the FDA is not in favor of obligatory labels, a voluntary system could be set up.

"I do reject mandatory government labelling, but I am in favor of voluntary labelling," said Elliot Entis, from the American Salmon Company.

And in a radical intervention Bruce Chassy, from the University of Illinois, said those consumers who did not want to eat GM foods should be prepared to pay more for their goods.

"All animals and plants we eat have been more altered genetically naturally, than by the human intentional genetic modification," he said.

He said it was the right of consumers not to eat transgenic food "but they have to pay the price for that because there is no difference scientifically established" and it costs more to grow conventional food.

If the FDA gives the salmon the go ahead it could also open the door to a variety of other kinds of genetically engineered animals ranging from tilapia to pigs to cows.

The FDA turned to the committee of independent experts after concluding earlier this month, based on company data, that the modified fish is safe for human consumption and the environment. It does not have to follow the committee's final recommendations.