Killer Fungus Strikes Montana Trout

A potentially deadly fungus is sweeping through a river in Montana, trashing the immune systems of local trout and making them increasingly susceptible to other illnesses. Local experts are worried that this could disrupt future populations in the area, as the fungus is disrupting spawning season.

Around this time every year, brown trout in Hole River near Melrose in southwest Montana can be found digging into their riverbed with their tails, creating spawning nests called redds.

However, the hard labor of making redds and the intense sparing matches that break out between males over the right to fertilize a clutch of eggs have been known to compromise a thin layer of slime that traditionally helps protect these fish from illnesses.

"The fungus is taking advantage of these fish when their ability to fight an infection like this is at its lowest point," Fisheries Manager Travis Horton of the Montana Fish, Wildlife and Parks (FWP) department explained in a statement.

However, he's quick to add that while this can be alarming, with anglers reporting small waves of dead brown trout washing up along the riverside, it's not yet a cause for concern.

That's because the fungus is naturally occurring in these spots, and has been frequently observed affecting parts of the river with denser populations of trout. You can even think of the fungus as a kind of population cap, Horton suggests.

"The important thing to remember is this is a system of stress," he added. "The fungus is natural and although the incidence is locally high, it isn't a cause for alarm."

Local biologists, however, are keeping a wary eye on the fungus - a grey and fibrous freshwater mold which appears to be especially prevalent this year. But Horton stipulates that Big Hole is simply experiencing a "perfect storm" of growing conditions.

Bitterroot-based fisheries biologist Chris Clancy also assured local fishermen that the fungus doesn't appear to be infecting any more trout than usual, despite its growth.

"Occasionally, a fisherman will see a fish not acting well in some quiet water and notice that it's covered in a growth that looks like cotton," Clancy told the Ravalli Republic.

But, he adds, it's nothing to lose sleep over.