ALMA -- A bacteria that kills gill tissue, limiting a fish^s ability to breathe, is believed to be the cause of death for 8,000 to 10,000 white bass recently at Harlan County Reservoir south of here.
Dean Rosenthal, assistant Fisheries Division administrator with the Nebraska Game and Parks Commission in Lincoln, said tests by the University of Nebraska - Lincoln Veterinary Diagnostic Center found Flexibacter columnaris bacteria in samples of fish collected from the lake.
"It^s a long, thin bacteria that develops externally and will spread across the fish," said Rosenthal, formerly a hatchery biologist with the Commission who worked with diseases. "It causes necrosis of the gills, which is basically the process of the death of cells or tissues within a living body."
Rosenthal said the bacteria was not found internally. A fungus was also found on the gills of affected fish, something believed to be a secondary infection.
Further tests will be done at the Bozeman (Mont.) Fish Health Center, the regional laboratory for the U.S. Fish and Wildlife Services, and results should be known in a month or so.
The bacteria is naturally occurring and fish die-offs are not uncommon.
Columnaris resulted in a die off of about a half-million crappie at Branched Oak Lake near Lincoln in 1984. Commission Fisheries Biologist Jeff Jackson of Lincoln said it could have been the cause of a die off of white bass at Pawnee Lake near Lincoln in 1994. In that instance, only a few hundred dead fish were observed, but sampling later that fall showed it was much worse when a dramatic population decline of white bass in the lake was observed.
The bacteria usually causes problems during times when fish are stressed. Commission Fisheries Biologist Brad Newcomb of Kearney said it is believed the white bass at Harlan were stressed when high winds and hot weather caused water temperatures in the lake to jump from 74 to 80 degrees during the week prior to July 4 -- the day dead fish started appearing.
"That^s one condition that can lead to these problems," Newcomb said, adding that rapid increases in water temperature aren^t uncommon in Nebraska^s wind-swept reservoirs.
"Even with that rapid of an increase, a lot of times we see no problems at all. It^s one of those naturally occurring things that so many factors go into, we don^t understand it very well and therefore predictions are impossible."
Newcomb said he believes few fish have died since July 8. But as was the case at Pawnee Lake, it won^t be known until fall sampling if the die off was more extensive than currently thought.
Newcomb said while the die off may sound big, it is estimated that 70,000 fish were harvested from the lake last year. "Any time you have 10,000 fish die, it^s a concern, without any question," he said. "But in the overall picture of the lake, they should be able to recover without any trouble."
Columnaris is not harmful to humans. Dead fish should not be eaten, but any healthy fish that are caught can be prepared as usual and consumed, Rosenthal said. Any lesions found on fish should be cut away before cooking, but Rosenthal said he doesn^t believe many will be seen.