The response has been so strong in the past two months that the FDA was asked to extend the public comment period, and it issued a statement Wednesday to say comments will remain open an additional 60 days, until April 26.
Morgan Liscinsky, spokesperson for the FDA, said the agency will review the comments after that and decide how to proceed.
"FDA will complete the review of the AquAdvantage Salmon application and will reach a decision on approval," Liscinsky said in an email.
"At this point it is not possible to predict a timeline for when these decisions will be made."
Developed at Memorial University in Newfoundland and the University of Toronto, the eggs are produced at AquaBounty Farms in Prince Edward Island and the fish are reared in Panama.
The Atlantic salmon egg is modified with genes from chinook salmon and an eel-like fish called the ocean pout, which makes the fish grow twice as fast as conventional fish, cutting in half the time it takes to reach market size.
Calls to Massachusetts-based AquaBounty Technologies, the company that wants to produce AquAdvantage commercially, were not immediately returned.
While genetically modified plant crops were approved for human consumption almost two decades ago, the altered salmon would be the first transgenic animal to make it onto a menu. The product has been making its way through the American regulatory process for 17 years.
Two reports issued by the FDA in December found the fish posed no significant impact on the environment south of the border, but the agency does not weigh ethics or policy around biotech foods as part of the regulatory process.
Alaska state lawmakers have vowed to fight approval of the so-called "frankenfish," alongside opponents like Lucy Sharratt, of the Canadian Biotechnology Action Network.
"The FDA has extended the comment period because this (genetically engineered) salmon is politically important and highly controversial inside the US. ... The extension signals heightened tensions," Sharratt said in an email.
She said the public concerns expressed in thousands of comments were not taken into account in the preliminary reports issued in December.
"Groups are hoping that the FDA will now take this chance to decide to publish a ... much more comprehensive review," Sharratt said.