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Some Big Hole Trout Affected by Fungus

Fish & Wildlife - Region 3

Tuesday, October 14, 2014

Anglers report seeing dead brown trout in the Big Hole River near Melrose in southwest Montana. The fish are noted to have a fungal infection known as saprolegnia.

Brown trout are susceptible to the fungus this time of year because they are stressed from spawning which may also result in depressed immune systems. Specifically, brown trout in high density areas like the Big Hole are digging in the river bottom with their tails to create their spawning nests (known as redds). They are also often fighting and bumping into each other causing them to lose or compromise the layer of slime which helps protect them from disease.

Region 3 Fisheries Manager Travis Horton says, “The fungus is taking advantage of these fish when their ability to fight an infection like this is at its lowest point.” However, Horton adds that this is not entirely unusual as there are occasional “hot spots” for saprolegnia and they are typically short-lived.

“The important thing to remember is this is a system of stress,” says Horton. “The fungus is natural and although the incidence is locally high, it isn’t a cause for alarm."