AquaBounty's president, Ronald Stotish, says the company has addressed these concerns by making the fish sterile, prohibiting mating with wild fish, and by growing them only in indoor tanks. Stotish says there's an environmental benefit to this approach: producers can grow salmon closer to where the fish will be sold, reducing transportation costs.

But not everyone agrees. "Land-based aquaculture uses huge amounts of water and energy to keep that water flowing," says Anne Kapuscinski, professor of sustainability science at Dartmouth College. "I am really skeptical that companies can make money raising salmon in a highly contained land-based facility."

Kapuscinski also worries that requirements limiting farming of the fish to pools on land will not adequately contain the risk of escape. "What about other countries? Salmon farming is global," she says, with large farms in Chile and Tasmania. "If it's not highly regulated and carefully contained, there could still be cases of escape."

For consumers, the primary concern is likely whether the fish are safe to eat. Stotish says that extensive testing shows that the nutritional content of the engineered fish is the same as that of traditionally bred Atlantic salmon. It also has no greater likelihood of prompting allergic reactions, he adds.

While it's unclear how consumers would respond to engineered salmon, the fish farming industry appears pessimistic. Trade groups--which are already sensitive to criticism of their industry--such as the International Salmon Farmers Association, the Canadian Aquaculture Industry Alliance, and the British Columbia Salmon Farmers Association, have come out against the commercial use of genetically modified salmon. "We don't support production of transgenic fish for food consumption until it has been proven safe and the market demands it," says Ruth Salmon (yes, that is her name), executive director of the Canadian Aquaculture Industry Alliance. "We have not seen any market demand at this time."

AquaBounty's long journey--the company first filed for regulatory approval in 1995--highlights the challenge of commercializing transgenic animals for food. It was only in 2008 that the FDA outlined how it would regulate genetically engineered animals meant for human consumption; rather than being reviewed like other foods, they are regulated as new animal drugs, reflecting their strange status in the regulatory landscape.

Some scientists say these hurdles have slowed down the field, and may push cutting-edge research to other countries. For instance, James Murray, a professor of animal science at the University of California, Davis, has genetically engineered goats that produce a human immune protein, which he hopes will help children suffering from severe diarrhea. He has moved some of his research to Brazil, which he says has enacted regulation and offered funding to support research and commercialization of transgenic animals.