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March 28, 2024 7:20 pm
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NDOW removing nonnative fish from Muddy River

Moapa Valley Progress

Potassium Permanganate being added to the river turning the water purple. The color is temporary. The substance is used to eradicate invasive fish species in the river.

As part of its 5-year effort to protect native fish populations in the Muddy River, the Nevada Department of Wildlife is conducting a nonnative fish eradication project using the chemical rotenone in the lower section of the river. The project is scheduled to begin Friday, March 22.

“The goal of this project is to eradicate nonnative blue tilapia (Oreochromis aurea) and other nonnative fishes in the Muddy River in an effort to conserve and recover imperiled, native fishes. This treatment is the last of three main-stem Muddy River treatments planned under our 5-year eradication project,” said Brandon Senger, supervising fisheries biologist for NDOW.

The blue tilapia is a predatory species that originates in North Africa and preys upon the endangered Moapa Dace (Moapa coriacea) and other native fishes. Tilapia were first reported in the Muddy River in 1991, but the invasive species quickly expanded its range throughout the drainage and had a significant impact on native fish populations.

“Removal of tilapia is an essential step toward removing threats to Moapa Dace and other Muddy River native fishes,” said Amos Rehm, the Muddy River fisheries biologist for NDOW. “Mechanical removal and other physical methods are not adequate to control blue tilapia, so we are using rotenone.”

NDOW worker applies Rotenone in an attempt to eradicate invasive species of fish.

Rotenone is a naturally occurring substance derived from the roots of a South American plant, and has been used historically by indigenous tribes as a method to capture fish, Rehm explained. “Since 1934, it has been safely used as a fisheries management tool, and has a long history of successful applications.”

Due to the large scale nature of the eradication effort, biologists have taken a systematic approach, focusing their eradication efforts on relatively small sections of the Muddy River at a time. Their focus for this phase of the project is that portion of the river that begins near Hidden Valley Road and ends at the Wells Siding Diversion.

During the project, a downstream section of the river will turn shades of red and purple, but there is no need for alarm, Rehm said. The purple coloring is caused by

Potassium permanganate, a water purifier commonly used to neutralize rotenone. The color change is temporary.

At concentrations used in fisheries management applications, rotenone is lethal only to gill breathing organisms like fish or early-stage amphibians and has no lethal or harmful effects on non-aquatic wildlife. To lessen the impact of the project on native fishes, biologists have spent the past several months salvaging native fish out of the treatment area and moving them to previously treated portions of the river.

NDOW has successfully used rotenone as a fish toxicant on many projects with no issues relating to human safety, recreation, irrigation, or livestock. According to Senger, “rotenone breaks down naturally in the environment through exposure to sunlight, water, heat and its own natural decomposition process.”

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