Conservation Issue

Invasive non-native fish species pose significant threats to aquatic ecosystems, often outcompeting native species for resources, disrupting food webs, and altering habitats. These invasive species can lead to declines in native fish populations and long-term ecological imbalances. Non-native fish such as common carp and brook trout are able to outcompete native trout or other native species in many places where they have been stocked in the western United States. A new technology, referred to as “Trojan Male” or “YY” Fish, can eradicate unwanted fish populations by incrementally eliminating female non-native fish, while leaving the existing native or desirable fish unharmed.

Trojan Male Fish Approach

Like mammals, most fish species have two sex chromosomes: X and Y. A natural genetic female will have two X chromosomes (XX), and a natural genetic male will have one X and one Y chromosome (XY). In the development of YY brood stocks, very young fish are exposed to the female hormone estradiol in their feed at a specific level and for a specific length of time. The treatment makes the male fish become egg-producers, but they are still genetically male. These egg-producing males are then bred with normal XY males, which means 25% of the offspring will have two Y chromosomes, hence referred to as YY males. Some YY males produced in that generation are exposed to estradiol, which then converts them into egg-producing YY males. This process allows a hatchery to have a group of egg-producing YY males and a group of sperm-producing YY males, which are kept for brood stock. After that, hormone treatment is unnecessary because only Y chromosomes are present in the eggs and sperm of the brood stock, and all of the offspring will be YY males. These YY offspring are stocked into target areas where the undesirable population will eventually shift to all males, because when the YY fish breed with natural XX females, their offspring will all be normal XY males.  Eventually, no females will remain in the population, preventing any further reproduction by the invasive species.

Benefits to Anglers

This technique has advantages over traditional non-native fish control methods due to the selective nature of the approach that allows desirable species to remain in a location for recreational or conservation purposes while the undesirable species are simultaneously eliminated.  This targeted approach not only protects native species but also eliminates the need for chemical treatments to eradicate non-native fish, so densities of fish and angling opportunities are maintained throughout the process.

Why WAFWA?

WAFWA is leading YY Fish efforts due to our organization’s ability to coordinate and leverage activities by various member states and agencies using this technology.  While YY Brook Trout are the first established and utilized brood stock, this approach has promise for a wide variety of species.  Aligning the needs of various agencies for YY fish with production and development from participant brood stock sources allows all member agencies to benefit.