AquaBounty Technologies expects regulatory approval by the fourth quarter of this year to produce its controversial genetically engineered salmon, its chief executive said on Tuesday.

"There have been no new legal issues, no new regulatory issues, no new environmental issues raised," AquaBounty Technologies Chief Executive Ronald Stotish said on the sidelines of the BIO International Convention. "We should have approval before the end of the year."

The U.S. Food and Drug Administration is due to close a public comment period on Friday and will then likely take 30 to 60 days to review the comments, which include heavy opposition from consumer and environmental groups.

It could take another 120 days after that for the FDA to issue final approval, Stotish said.

"We're hopeful that the FDA will conclude the process," he said. "We can go on then and begin to grow our business."

The salmon, trade named AquAdvantage, would be an all-female population with eggs produced in a facility on Prince Edward Island in Canada and shipped to a "grow-out facility" in Panama, where they would be reared to market size and harvested for processing.

AquAdvantage salmon eggs are engineered to produce fish with the potential to grow to market size in half the time of conventional salmon. If it gets a final go-ahead, it would be the first food from a transgenic animal, one whose genome has been altered, to be approved by the FDA.

Some have threatened to sue if the fish is approved. It would be the first genetically engineered animal commercialized in the food supply.

Stotish said he fully expected litigation to try to stop commercialization, but he said the FDA had been working to fully document the record on its assessment of the genetically engineered salmon to protect against court challenges.

Stotish said AquaBounty has explored legal recourse if the approval is not granted.

AquaBounty was close to financial demise as recently as last fall and lost more than $4 million in 2012. A new investor and a fresh $6 million in capital raised this spring has extended the company's life for at least another year and a half.

"This project has gone on far too long," said Stotish. "Our product has significant cost and economic benefits and we believe environmental benefits. Instead of importing 500 million pounds of salmon we can grow some of that right here. That is good for the consumer. We think that is good for our economy."

In a draft environmental assessment issued in December, the FDA affirmed earlier findings that the biotech salmon was not likely to be harmful and said the agency had concluded that food from AquAdvantage salmon was as safe as food from conventional Atlantic salmon.

Critics have said the genetically engineered salmon is a dangerous "experiment" and they have pressured the FDA to reject it. They have said the FDA has relied on outdated science and substandard methods to assess the fish.

Whole Foods Market, Trader Joe's and other food retailers representing more than 2,000 U.S. stores have vowed not to sell genetically engineered seafood if it is approved in the United States.