While opponents are calling this the Frankenfish, other experts on nutrition say we should be more afraid of the average supermarket chicken.
That's because the practice of feeding grain to chickens, as well as cows and tilapia, radically alters the nutritional profile of the meat, while the genetic alterations in the new salmon seem to show little effect.
Salmon can't live on grain, so the farmed variety still contain a healthy dose of the good fats known as omega-3 fatty acids, said biochemist Floyd Chilton of Wake Forest University. If genetic modification can make omega-3 rich salmon cheaper and more available to low-income families, he said, it could offer a big public health benefit.
Last month, the FDA announced that it had reviewed the company's research and declared the fish safe for consumption, a step that makes approval seem inevitable. But opponents sounded the alarm, claiming that the research was inadequate and that approval would set a precedent, allowing other genetically modified animals to get into restaurants and supermarkets unmarked.
In response to all the concerns, the FDA held hearings two weeks ago in Washington. The Veterinary Medicine Advisory Committee heard testimony on health and environmental hazards and the possibility of requiring labeling so consumers would know if they were buying transgenic fish.
The salmon's creator, California-based AquaBounty Technologies, started with farmed Atlantic salmon. Researchers found they could induce the fish to reach market size in half the normal time by adding genes from a chinook salmon, a distinct species, and a cold-water, eellike fish called an eelpout.
The fish don't ultimately grow bigger than ordinary salmon, said AquaBounty research and development director John Buchanan.
The growth hormone gene came from a chinook salmon, a Pacific species, because Canadian researchers had already learned to isolate this gene, clone it in bacteria, and read its sequence of genetic code, Buchanan said.
Scientists suspected it would work in Atlantic salmon because the code for that particular gene was so similar in the two fish.
The other gene they added is called a promoter because its job is to act as a switch to turn the growth hormone gene on and off. The promoter comes from the eelpout, which lives in very cold waters. The promoter turns on a gene that makes a kind of antifreeze chemical.
In the genetically modified salmon, the same promoter has a different job: keeping the growth hormone gene turned on all the time. In ordinary Atlantic salmon, the gene is switched on only during summer months.
Why a promoter associated with an antifreeze gene from an eelpout? That gene was already available, having been isolated and cloned in earlier work aimed at creating more cold-resistant fish, Buchanan said.
The AquaBounty people also manipulate the sex chromosomes of the salmon in order to render them sterile.
The process starts by changing the sex of some female fish. Using a form of testosterone, biologists can produce a malelike fish called a neomale, which looks and acts like a male and produces sperm. The only difference is the neomales produce only female offspring, thanks to their female genetics.
By allowing the neomales to mate, the AquaBounty researchers can produce batches of eggs that are all female. These they can alter by applying a source of physical pressure. That disrupts the normal process of fertilization, leaving the eggs with three copies of each chromosome instead of the normal two.
Weird as it sounds, that's done all the time in farmed fish, Buchanan said, to keep them from reproducing with wild stocks if they escape.
In addition to this procedure, he said, the company is using physical barriers to isolate the fish. They're being raised in ponds in the highlands of Panama, where local waters don't support salmon.
Buchanan said all this genetic tinkering should make it more economical to farm fish in tanks and ponds on land. Dwindling stocks of wild fish can't meet the nutritional demands of a growing population, he said. "One way to relieve the pressure is more efficient aquaculture."
He said raising fish on land reduces several problems typical of traditional fish farming: pollution of local waterways with waste and antibiotics, transfer of parasites from farmed to wild fish, and the escape of fish.
To meet FDA requirements the company, he said, did "exhaustive" studies on the fish's composition, the fats and amino acids and vitamins.
Biologist Michael Hansen of Consumers Union says the studies don't go nearly far enough. "It's a very flawed safety assessment," he said, adding that the samples were too small, and that the results revealed a possible increase in allergy-causing proteins.
"Fin fish are a major source of food allergies," he said. He was concerned that the growth hormone gene from the chinook salmon might trigger allergies in people who are otherwise able to eat Atlantic salmon, he said.
Hansen said that although he believed there was no danger from excess growth hormone in the salmon, he thought the company's studies weren't adequate to show this.
And the company failed to look at factors that might degrade the health of the fish, making them more vulnerable to parasites or leading to more use of antibiotics.
"This is a very bad data package. I'm stunned by the poor quality of it," Hansen said.
The fish may also pose a danger to the environment if their production is scaled up, said Anne Kapuscinski, professor of sustainability science at Dartmouth University, who also testified last month.
The operation that AquaBounty is proposing is relatively small, she said, but FDA approval could set a precedent for large-scale production of transgenic fish, and eventually some of those fish could escape and breed, changing the gene pool of the wild population irreversibly.
The way they make the fish sterile isn't foolproof, she said. It works more than 99 percent of the time, but if they're farming tens of thousands of fish, that means hundreds will remain fertile.
The world consumes 1.4 million tons of farmed salmon a year, Kapuscinski said, so if genetic modification becomes widespread, it's only a matter of time before salmon escape.
They might breed with existing species or they might become invasive, outcompeting other fish.
In general, she said, farmed salmon put more burden on the environment than does fishing for wild salmon. Farmed salmon must be fed on seafood, often wild fish. And many farmed fish produce wastes and develop diseases that leak into waterways and affect wild fish.
Others say the FDA should weigh risks and benefits. Salmon are one of the few remaining sources of a form of those important good fats, the omega-3 fatty acids, said Wake Forest's Chilton.
Several studies have shown that low intake of this type of fat is associated with heart disease and possibly dementia and aging.
Chilton's studies show that farmed tilapia have almost no omega-3 fatty acids, no more than the same amount of beef. Plant-eating animals build up omega-3's from eating food with chlorophyll, but that plummets when they're fed grain, as are most cattle, chickens, and tilapia.
Farmed salmon carry less omega-3 than does the wild type, but still much more than many other fish, and far more than factory-farmed chicken or beef, Chilton said.
"There's this cry out there that these genetically engineered fish are not natural," he said. "But there's nothing natural about the fatty acid composition of most of the animals we eat."
Selective breeding and grain feeding have added to the depletion of omega 3s, he said; chicken and beef have just a fraction of what they used to.
"Right now, a large segment of our population can't afford the most important nutrient they could be getting," he said.
If we can't feed the world on grass-fed beef and wild salmon, he said, perhaps we must look to genetic engineering to replenish the good fats in the food we eat.
Buchanan of AquaBounty said the company expects a decision by the FDA before the end of the year. One likely compromise would be to allow the fish on the market but require labeling. The FDA may do that, though Buchanan said there was no precedent for such a requirement, since the composition of the transgenic fish is identical to ordinary salmon.
AquaBounty, he said, would encourage those selling the fish to label it, though that decision is up to those growing the fish and those selling it to consumers.
Contact staff writer Faye Flam at 215-854-4977 or firstname.lastname@example.org.