It’s all in the genes: how water pollution keeps silver carp at bay.
Jeffrey, J. D., K. M. Jeffries, and C. D. Suski. 2019. Physiological status of silver carp (Hypophthalmichthys molitrix) in the Illinois River: An assessment of fish at the leading edge of the invasion front. Comparative Biochemistry and Physiology Part D: Genomics and Proteomics 32:100614. https://doi.org/10.1016/j.cbd.2019.100614
What’s a Silver Carp?
Silver carp are a common aquatic invasive fish species found throughout the Mississippi River Basin in the United States. Brought to Arkansas from Asia in the 1970s to control algae growth, silver carp are now notoriously known for their ability to destroy healthy aquatic habitats by out-competing native fish species. You may also recognize silver carp by their propensity to leap out of the water when they are frightened or startled, which has led to many injuries of fishermen, folks engaged in water sports, and casual boaters. Silver carp abundance has sky-rocketed since their introduction, and their range has increased throughout the Mississippi River and its tributaries. Currently, silver carp are at the brink of entering Lake Michigan via the Illinois River and the Chicago Area Waterway. The invasion of silver carp in the Great Lakes would decimate the recreational and commercial fisheries, which are an important part of the economy in the Great Lakes Region.
The Nitty Gritty
Interestingly, despite their history of spreading into nearby water bodies, silver carp have yet to enter Lake Michigan even though they have been on the verge of entering it for the past decade. A recent study led by Jennifer Jeffrey, a biologist at the University of Illinois, hypothesized that silver carp on the “leading edge” of the invasion, i.e. closest to Lake Michigan, may show clues within their physiology that explain why they haven’t reached Lake Michigan yet. The research group studied two sites within the silver carp population in the Illinois river: the leading edge, which is about 52 river miles downstream of Lake Michigan, and the core population in Havana, IL, which is about 146 river miles downstream of the leading edge. For each site, the researchers looked at genes in silver carp related to their stress levels and nutritional status. The research team also looked at genes related to DNA repair.
When compared to the core population, silver carp at the leading edge showed an upregulation of genes (increased response to a stimulus) related to defense against chemicals and cell death, and a downregulation of genes (decreased response to a stimulus) related to DNA repair. The genetic findings of the fish in the leading edge are consistent with fish that inhabit a polluted environment.
The Chicago Area Waterway System is a series of waterways around the Chicago region that ultimately connect the Great Lakes to the Mississippi River. Given its proximity to the populous city of Chicago, it comes as no surprise that the Chicago Area Waterway System has an issue with water pollution. According to contaminant testing done by the U.S. Geological Survey in 2015, the Chicago Area Waterway System region has a higher concentration of contaminants such as pharmaceuticals, wastewater, and volatile organic compounds than downstream in the Illinois River. These results correlate with the researchers’ findings that silver carp at the leading edge of the population, near the Chicago Area Waterway System, have physiological effects that likely resulted from polluted waters, versus the core population which did not display these physiological effects. As a result, this study suggests the water pollution in the Chicago area is actually keeping silver carp at bay and preventing their spread into the Great Lakes.
The Solution to Pollution
Currently, the Chicago area is beginning to implement programs to clean up its waterways and decrease litter and pollution. While the ultimate goals of these programs are useful and necessary, they may carry the unintended consequences of facilitating the movement of silver carp upstream and into Lake Michigan. If silver carp were to enter Lake Michigan, they would then have unfettered access to most of the eastern United States where they would likely continue to out-compete more native fish species.