The chemical at the heart of a massive pet food recall has turned up in fish hatchery feed in Oregon.

Melamine, which is used to make plastics, was detected in fish feed at the Marion Forks Hatchery in Idanha, according to the Oregon Department of Fish and Wildlife.

The tainted feed was used as a starter diet for young salmon and trout at Marion Forks, near Detroit Lake. The same lot of tainted feed was sent to six other Oregon hatcheries: Willamette, Gnat Creek, Big Creek, Cole Rivers, Butte Falls and Leaburg.

Farmed fish are usually sold for consumption or for stocking lakes and streams.

It wasn’t clear whether any of the fish ended up on U.S. dinner tables. Dr. David Acheson, food protection chief of the Food and Drug Administration, said the fish would pose a minimal health risk if any were eaten.

All of the hatchery managers have stopped using the feed, Oregon officials said.

Fish samples will be screened for signs of melamine, the FDA’s Acheson said.

“Depending upon what we find in that testing, that is going to drive the next steps,” he said.

The feed came from a Vancouver, British Columbia, company, Skretting Co., and was distributed under the Bio-Oregon label out of Longview, Wash., Oregon officials said.

The tainted ingredient in the feed was imported from China by ChemNutra Inc., based in Las Vegas. ChemNutra then sold the product to Skretting, which turned it into fish food and sold it to U.S. hatcheries, the FDA said Tuesday in a teleconference from Washington, D.C.

The FDA said it’s working with Canadian officials to track the tainted food.

While the Canadians made fish food with the tainted Chinese ingredient, U.S. companies manufactured pet food. Some food was mixed into feed at U.S. farms raising 6,000 pigs and 20 million chickens.

The U.S. Department of Agriculture will not approve any animals that ate tainted food for slaughter for human consumption.

In its teleconference, the FDA revealed another twist in the pet food recall: mislabeling. Acheson said testing revealed that the tainted ingredients labeled wheat gluten and rice protein concentrate were actually wheat flour.

The tainted ingredients came from two Chinese companies. FDA officials are investigating in China.

Regardless of the name, the ingredients contained melamine and cyanuric acid, a chemical used in swimming pools. Scientists suspect the interaction of the two compounds caused kidney failure in pets across the country.

It’s not known how many cats and dogs have died nationwide, although the FDA has received reports of more than 4,000 deaths.