The U.S. Food and Drug Administration said the level of melamine, which was implicated in the deaths of pets and sparked a huge recall of dog and cat food, didn't appear to pose a risk to humans or livestock, The Washington Post reported.
The level of melamine used in the fish feed was higher than in livestock feed but was very unlikely to pose a human health risk, the FDA said.
Tembec BTLSR of Toledo, Ohio, used melamine as a binding agent in feed granules that it sold to another company, Uniscope, which detected the ingredient in testing, the FDA announced.
FDA officials said they didn't know why Tembec didn't stop using melamine when the chemical received so much publicity during the pet food scandal.
"What they knew and didn't know before will be part of the investigation as it unfolds," David Acheson, the FDA's assistant commissioner for food protection, told the Post. "It's speculation in terms of motives and who knew what."