Population Control of Brook Trout with YY Males, by Jacob Beckner

Growing up in the Appalachian Mountains it was always remarkable when an avid trout angler would catch something other than a hatchery raised Rainbow Trout (Oncorhynchus mykiss), such as a native Brook Trout (Salvelinus fontinalis), or Brown Trout (Salmo trutta) as it can be seen in the figure on right. However, many residents located outside of the Appalachian Mountains would argue that species of Salmonids such as Brook Trout are invasive, and demand eradication to restore the natural aquatic ecosystems where they were introduced. Until now, one of the proven methods for limiting Brook Trout in non-native environments was to manually remove each individual from the affected stream. However, the Idaho Department of Fish and Game have recently developed a new method that is possibly more efficient. They have proposed a method to limit populations by engineering Brook Trout with the Trojan Y chromosome which would effectively skew the entire invasive population towards male. Therefore, this would limit the amount of fecundity drastically and eventually leads to very limited reproduction. However, before a full-scale stocking program can arise, many additional trials and experiments are needed along with proper permits from the Food and Safety Administration (FDA) (Schill et al. 2015).

Non-native Brook Trout being reeled in at Palmer Lake, Colorado.  Photo by Heath Alseike.   Creative Commons Flickr

Before it is deliberated on how exactly scientists are manipulating this invasive species within the family of Salmonidae, it is imperative that proper definitions are ascertained. Initially, according to The National Wildlife Federation an invasive species is any kind of living organism that is not native to an ecosystem and causes negative impacts on the environment. Many invasive species are labeled due to their rapid growth, fast reproduction, and potential to cause harm (The National Wildlife Federation). As it can be observed on this map Brook Trout have spread drastically outside of their native range (highlighted in orange), and due to anthropogenic disturbances and introductions to non-native streams they have spread to the areas highlighted in red.

Native (orange) and non-native (red) distribution of the Brook Trout in USA.  Source: USGS. 

Furthermore, since the definition of an invasive species has been properly established, one would inquire what precisely Brook Trout are doing to disturb their non-native environment? Originally, non-native Salmonids were introduced as a game fish in certain parts of the country to encourage indigenous angling in streams (as it can be seen on the left), and to lower the threat of over harvesting on native species of Trout such as Oncorhynchus mykiss in many parts of the western United States. However, as many Evolutionary Biologists would propose, selective pressures imposed on an environment have shaped organisms within the ecosystem, and when a non-native species is introduced to a new ecosystem it will either succeed immensely or be crushed instantly. After several generations, Brook Trout grew to be more harmful than beneficial to their new, non-native environments, and reproduced exponentially way beyond the original purpose. They began to out compete the other native Salmonids of the region which has led to the destruction of the aquatic fauna in the region (Schill et al. 2015)  along with immense competition for other resources within their environment.

As it was previously stated, researchers at the Idaho Department of Fish and Game have developed a method to create a population of Brook Trout with the Trojan Y Chromosome (TYC) which is designed to specifically skew the population toward all male. Therefore, placing detrimental selective pressures on the population (Schill et al. 2015). One of the most significant concepts of this process is to integrate concealed _Y chromosomal material into the populations by circulating males that are genetically _YY instead of _XY, along with males that are phenotypically female (F_XY) (Schill et al. 2015). Finally, the objective of this study was to primarily create genetic indicators to determine the sex of Brook Trout and to produce a fecundate population of salmonids comprised of phenotypic males and females whose development could be measured along with the completion of progeny examinations to ensure genetic accuracy (Schill et al 2015).

This process was completed in three stages and can be comprehended by the diagram to the right. First, exogenous estrogen was used to engineer trout with the genetic composition of M_YY, also called “Super-Males”. Secondly, to change the gender of half of the _YY males at the fry stage using estrogenic hormones to turn them into “Neo-Females” (F_YY), and lastly to preserve groups of both M_YY and F_YY as a means of producing large numbers of _YY fish into the wild (Schill et al. 2015). This technique of transforming a population from Males (XY) into phenotypically fecundate Females (XY), and then breeding them with Males (XY) who have been manipulated to become phenotypically fecundate males (YY). This has been proven to slope the long-term population of Brook Trout into an all-males by ensuring the reproduction by two males into male offspring. After the execution of this study, it was recognized that there was tremendous hope for the future of this program. The statistics for the sex determination proved very effective as ninety out of ninety (100%) genotypes matched the acknowledged phenotypes of the Brook Trout (Schill et al. 2015). Subsequently, at the completion of the first step of the study, which was releasing estradiol infused feed that feminized Males (M_XY) into Neo-Females (F_XY), it was shown that this method of production was ninety-six efficient in producing viable females (Schill et al. 2015).

After assessments of these experiments it is possible to anticipate what the future of these experiments could be. As of now, the total cost of rendering this program is around ten thousand dollars from establishment to completion, including feed, labor, and genetic testing (Schill, Daniel J., et al.). It can be documented that this is not a very costly or extraneous procedure as compared to manually removing the invasive Brook Trout from the non-native streams. It can also be concluded that once this method of population control is reputable and further studied it can be possibly used as a guide to limit populations of other invasive species. As depicted in the graph above, there are current issues in Yellowstone National Park due to the introduction of Lake Trout (Salvelinus namaycush), which have greatly reduced the number of native Cutthroat Trout (Oncorhynchus clarkii) in the area. Additionally, for this specific example, it can be acknowledged that this invasive species has further contributed in the ecological trophic cascade of the area (Middleton, Arthur, et al). However, if this method of sex manipulation by the Idaho Department of Game and Fish proves further effective, safe, and efficient, it can be concluded that it could also be introduced to Yellowstone. Hopefully, this method can lead to the restoration of the natural aquatic habitat of Yellow Stone National Park.

 

The author with Brook Trout. 

In conclusion, this analysis was designed and established to prove if there were better methods of restraining invasive species of Salmonids in tributaries on the northwestern portions of the United States that contained Brook Trout. The Idaho Department of Fish and Game has investigated to see if they could produce a viable idea to selectively limit the populations and reduce their specific fecundity. They developed a system that would manipulate Brook Trout using the Trojan Y Chromosome (TYC) to effectively limit the invasive growth of the population (Schill et al. 2015). Researchers then hypothesized and demonstrated that the complete population would inherently shift toward the male sex thus greatly reducing fecundity. The results from these examinations were very promising, proposing that similar trials could be performed in the future and that this can be applied as a method of population regulation on naturally occurring aquatic ecosystems pertaining the invasive Brook Trout.

References

Berkshire Outdoorsman. Accessed April 26, 2018. http://www.berkshireoutdoorsman.com/category/fishing/trout-fishing/.

"Invasive Species | National Wildlife Federation." The National Wildlife Federation. Accessed April 26, 2018. http://www.nwf.org/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Invasive-Species.

"Trout." White Oak Farm. January 24, 2017. Accessed April 26, 2018. https://whiteoakfarmny.com/trout/.

United States Geological Survey. Brook Trout (Salvelinus fontinalis) - Species Profile. Accessed April 26, 2018. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=939.

"Case Studies of Lake Trout and Cutthroat Trout Interactions." Accessed April 26, 2018. http://www.cfr.washington.edu/classes.esrm.459/yellowstone/cutthroat/wildlife.htm.

Middleton, Arthur. "Is the Wolf a Real American Hero?"  March 09, 2014. Accessed April 26, 2018. https://www.nytimes.com/2014/03/10/opinion/is-the-wolf-a-real-american-hero.html.

Schill, Daniel J., Jeff A. Heindel, Matthew R. Campbell, Kevin A. Meyer, and Elizabeth R. J. M. Mamer.  2015. Production of a YY Male Brook Trout Broodstock for Potential Eradication of Undesired Brook Trout Populations. North American Journal of Aquaculture 78: 72-83.