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In western US waterways, invasive and voracious brook trout are outcompeting native species - but a modified variant could tip the scales

On a golden morning in early October, two graduate students from New Mexico State University plunge into the icy current of Leandro Creek. The small waterway flows through the 550,000 acre Vermejo park ranch, a reserve in the Sangre de Cristo Mountains, and the pair are in search of an unusual fish.

Kelsie Field, 25, from the Department of Wildlife and Conservation Ecology, wears a pair of worn grey waders and carries two eight-gallon buckets, one full of water, the other, of scientific gear: test tubes, an electronic scanner and surgical implements. Michael Miller, 30, shoulders a large, waterproof backpack containing a battery attached to an electrode that resembles a metal detector.

Researchers Kelsie Field and Michael Miller go electrofishing' in New Mexico. Photograph: Jeremy Miller