Instead, the tests confirm the initial diagnosis that two bacterial infections, Columnaris and Aeromonas, caused the catfish to die.
According to Ling Shen, fish health specialist for the Minnesota Department of Natural Resources in St. Paul, a nearly dead catfish sent to the DNR's pathology lab in early September tested positive for both bacteria, which occur naturally in the water.
Meanwhile, two other fish caught by Grand Forks anglers and collected by DNR staff for testing a few weeks later showed skin lesions, Shen said, but were in better condition than the first catfish tested. Neither of the fish had Columnaris bacteria on their gills, she said, and none of the internal organs tested positive for the Aeromonas bacteria.
It's likely a combination of environmental factors, including high water temperatures and low river flows in the weeks leading up to the die-off, weakened the immune systems of the catfish, making them more susceptible to infection.
Tests rule out deadly viruses in channel catfish die-off
US - Additional pathology tests have ruled out two deadly fish viruses - Viral Hemorrhagic Septicemia (VHS) and Channel Catfish Virus - as causes of a die-off that killed thousands of catfish in early September along the Red River south of Grand Forks.