The Food and Drug Administration is still considering whether a proposed genetically engineered fish is safe for consumers, the agency's top official said on Thursday.

FDA Commissioner Margaret Hamburg said it was examining as many as 35,000 comments about the application on the salmon by Boston-based AquaBounty Technologies Inc, which applied for approval in the mid-1990s.

"We will be moving forward in a deliberate, science-driven way, reflecting all of the important inputs ... as we consider this product application," Hamburg told the U.S. Senate's Health, Education, Labor and Pensions Committee during a hearing about the agency's current initiatives.

AquaBounty officials could not be reached for comment. The company has said in the past that it expected a decision from the FDA by the end of 2013.

Hamburg did not say when the FDA would make its final decision.

If the altered fish, known as AdquAdvantage salmon, is approved, it would be the first genetically altered animal product to reach the plates of consumers in the United States.

The company has said its salmon is safe to eat and could help address numerous food supply issues, including the demand for healthier foods and depleted fish stocks, because it is engineered to grow more quickly.

But environmental, health and consumer advocates have raised concerns, citing unknown long-term effects on people and the planet of a genetically altered food.

Republican Senator Lisa Murkowski of Alaska told Hamburg she wanted assurances that the agency would not allow the fish to be sold if it could not determine it was safe. She also said if the agency does approve it, the fish should carry clear labeling to show it is genetically altered.

"I don't believe that the FDA has adequately studied the environmental effects, the economic impacts ... let alone the potential health impacts on humans," said Murkowski, whose state is home to a significant fishing industry.

"If we could guarantee that it wasn't safe to eat, then it would not pass our approval standards," Hamburg said.