Officials investigating a Red River catfish die-off are testing for viruses - to rule them out. They believe the culprit is a bacterial infection.

Technicians at the Minnesota Department of Natural Resources pathology lab in St. Paul are testing for the viral hemorrhagic septicemia virus, which can cause a wide range of trophy fish, including walleye and bass, to bleed to death. The virus has not yet been found in North Dakota or Minnesota.

"It's just routine," said Henry Drewes, a regional fisheries supervisor for DNR. "The preliminary assessment seems to be pointing at columnaris, a bacterial infection."

Channel catfish virus also is a possible cause, said Lynn Schlueter, Red River fisheries biologist with the North Dakota Game and Fish Department.

The virus normally occurs in hatcheries where a lot of fish are confined, but Schlueter said it can strike in the wild if conditions are right. He compared it to winning the lottery - "just getting that perfect combination (of conditions) that really allows it to take off."

Larry Hanson, a catfish virus expert at Mississippi State University's Fish Diagnostic Laboratory, said he is not aware of any reported cases of the virus in the wild. "It's almost always in a hatchery environment under crowded conditions," he said.

"It's the time of the year where you would see it, but generally it's under warm conditions, and rivers are usually not as warm as a (hatchery) pond environment is," Hanson said.

The virus also is rare in larger, older catfish, he said. Some of the dead catfish were 30 inches long.

An estimated 1,600 catfish died in the Grand Forks area. Officials were first notified by a fishing guide who spotted dead fish last weekend. The Red River forms the border between Minnesota and North Dakota, and wildlife officials from both states are investigating.

The die-off appears to be confined to the Grand Forks area.