Farmed fish that may have eaten food with imported Chinese ingredients show no traces of contamination and should be safe to eat, the Food and Drug Administration said Thursday.

The two fish farms that used the feed kept their fish off the market until the tests could be completed.

Dr. David Acheson, assistant commissioner for food protection, said fish being raised at Kona Blue in Hawaii and American Gold Seafoods in Washington state were found negative for the chemical melamine.

The questionable feed was also sold to 196 fish hatcheries. Because those fish are small and the feed has been recalled, Acheson said the FDA believes there no longer is any public health concern from them.

The FDA on Tuesday cleared for use 56,000 pigs given feed that included scraps of pet food contaminated with melamine.

Melamine contamination has been blamed for the deaths of an unknown number of dogs and cats, resulting in the recall of dozens of pet food brands.

Since the problem was discovered, 46 shipments of protein concentrate from China have been detained and are being held until the companies that produced them can prove the material is free of melamine, Acheson said.

"Any vegetable protein concentrate from China is not going to be imported until we are sure that it is negative," Acheson said.

He said fish imported from China are being tested for melamine.

In the longer term, he added, his agency is working with Chinese authorities on ways to make sure this does not happen again.

Vera Adams, executive director for commercial targeting and enforcement at Customs and Border Protection, said her agency has begun testing imported wheat, corn and rice protein concentrates from all countries.

She said samples from about 80 percent of shippers have been tested. Eighty-percent of the testing is complete and turned up no melamine contamination.