Invasive Brook Trout have been plaguing the American West’s native fish since they were introduced. They out-compete native cutthroat trout for food and spawning areas and have taken over many historically native waterways. But researchers have developed a new method to prevent their spread: a sex change.

Every trout, just like humans, has genetic markers that determine their sex, either XY (male) or XX (female) and according to a study released by the American Fisheries Society, the males can be feminized by exposing them to estrogen. And by breeding these “feminized” males, a YY male trout can be produced. These YY trout are then introduced into the wild. But this is where it gets interesting when the YY males spawn with an XX female, 100% of their offspring will be almost 100% XY males. The idea is this, that over time as these fish continue to spawn, eventually the entire population will be male and then die out.

The results so far, tested in Idaho’s Big Lost River watershed, have been promising with the Trojan Males (YY) spawning and creating the intended, predominately male, new (and hopefully final) generation of brook trout. Which will, in turn, allow the native cutthroat to once again recolonize their lost territory.

To read more about the project, check out the full article on!

Source: Hatch Mag.

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