Trout swim in a viewing pond at the Nevin Hatchery in Fitchburg near Madison, where some fish tested positive for cutthroat trout virus.
State natural resource officials are wondering how a mysterious virus found its way to Wisconsin trout and what it will mean for the health of aquatic life.
"It's a big unknown," said Susan Marcquenski, a fish health specialist for the state Department of Natural Resources. "There's very little information about the effect of the virus on cool-water species."
Despite the uncertainty, state authorities confirm that they released 270,000 brown trout this year from hatcheries where fish tested positive for the cutthroat trout virus. An additional 160,000 had already been released last ...