Trojan trout: could turning an invasive fish into a ‘super-male’ save a native species?

Brook trout may greatly outnumber the Rio Grande cutthroat here, but nearly every brookie the team captures is male. That’s because many are a lab-produced variety known as “Trojan” brook trout. They are unique in that they carry not one, but two copies of the Y chromosome that codes maleness; they have no X chromosome to pass on. Since 2018, various streams across the Vermejo reserve have been stocked with this strain in an attempt to tilt the brook trout sex ratio so far male that eventually the population will stop breeding and die out on its own. Similar efforts are under way in a handful of creeks in Idaho, Washington and Oregon, and Nevada plans to embark on its own stocking programme this summer. Until now, the main tool to eliminate invasive fish species has been the potent chemical rotenone. The trouble is that “it also kills all the other fish, including the ones you are trying to conserve,” says Colleen Caldwell, a professor of fish and wildlife at New Mexico State University and a principal investigator overseeing the Leandro Creek project.

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