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Sex-Altering Hormone Used as Control Method for Brook Trout

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This high-tech way of controlling unwanted populations of  brook trout is the first of its kind.

The Idaho Department of Fish and Game has been experimenting with a sex-altering hormone in order to help successfully manage local populations of brook trout, according to

The experiments use the a female hormone named estradiol to affect sex in a segment of the fish population. Once this is completed they then “breed them to get and entire population to produce one sex.”

The technology is decades old and has been used in fish hatchery scenarios to raise higher quality fish for food consumption.

The Idaho Department of Fish and Game is hoping to be able to determine whether or not this technology can be implemented in eradication efforts of not only the local brook trout, but other unwanted fish populations in other areas of the country.

brook trout
Photo by: Backwater Fly Fishing

Brook trout were deliberately introduced in to the West in the 1800s. The big concern is not for the brook trout, but the way they affect other fish populations in the waters they inhabit, especially the native cutthroat.

In areas where the two coexist, biologists typically report a drop in the number of cutthroat. This is at the heart of the effort to diminish the brook trout population.

It seems that existing methods for getting rid of fish like using chemicals, netting, or electrofishing are only temporary solutions since some fish escape and spawn the following year. Then you are back to square one. This is where the YY-males are expected to shine.

“Stocking YY-male hatchery fish into a body of water with an undesired fish population could change the sex ratio to all males within a few generations, and the unwanted fish population would eventually fail to reproduce and therefore die off. Once accomplished, Fish and Game would stop stocking those fish and fisheries managers would then restock that body of water with a more desirable fish species,” the agency stated.

Four streams have been stocked so far in the state and monitoring efforts are underway.

“The proof will be in the pudding over the next few years when our research staff obtain results confirming whether stocked YY fish successfully spawn in the wild and are ultimately effective in reducing the percentage of wild female brook trout in test waters,” stated Dan Schill, fisheries research supervisor at Fish and Game. 

“We really won’t expect to see a big effect on sex ratio until two or three years go by,” Schill said.


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Sex-Altering Hormone Used as Control Method for Brook Trout