High Rate of Tumors Found on white sucker in some Wisconsin Rivers


There is an elevated incidence of skin and liver tumors among White Suckers caught in certain Wisconsin rivers that flow into Lake Michigan according to a U.S. Geological Survey study recently published in the Journal of Fish Diseases.

The three-year study looked at White Sucker tumor prevalence in the Sheboygan River and Milwaukee Estuary, which have both been listed as “Areas of Concern” under the International Joint Commission Great Lakes Water Quality Agreement between the United States and Canada. According to this agreement, “an AOC is a geographic area designated by the [the United States and Canada] where significant impairment of beneficial uses has occurred as a result of human activities at the local level.”

In accordance with the agreement, any part of the Great Lakes, or it’s tributary rivers, can be listed as an AOC if special criteria are met. One of the 14 criteria used for labeling an AOC is the pervasiveness of tumors on certain species of fish, including White Sucker.

 Lip tumor diagnosed as a papilloma on a white sucker fish

 Lip tumor diagnosed as a papilloma on a White Sucker, USGS

Once an AOC has been listed, the agreement requires a Remedial Action Plan to be developed that will restore impacted areas. As part of a remedial action plan, the State of Wisconsin asked the USGS to acquire data about the status of White Sucker within the two AOCs that were used in the study. During the research period, which lasted from 2012-2014, approximately 200 adult suckers were collected at each site during the fish’s migration periods. Fish were also collected in two non-AOCs, the Root River and Kewaunee Rivers, for comparison.

After compiling the study data, researchers revealed there was an abundance of liver tumors and skin lesions on the bodies, fins and lips of fish collected from three of the four sites.

“There was an elevated prevalence of skin and liver tumors on fish from both Areas of Concern as well as one of the non-Areas of Concern,” said Vicki Blazer, USGS Research Fish Biologist and lead author of the study.

Discovering elevated levels of fish tumors in an area not designated as an AOC was not unexpected, said Blazer. The research scientist said this non-AOC, the Root River, is close to the Milwaukee River, which has similar land and industrial runoff as the two AOCs.

However, the research team did discover something they weren’t initially looking for as they were examining their specimens.

Some of the male fish collected at both AOCs had testicular tumors in addition to the skin and liver tumors the scientists were documenting. The data collected did not show a correlation to the frequency of liver and skin tumors between male and female suckers, therefore, the testicular tumor finding was the only discovery directly related to the sex of tested fish.  

While the rates of liver and skin tumors seem to be equal between male and female fishes, the age of the fish does seem to play an important role in tumor development.

“Many of the fish with the skin and liver tumors were fairly old,” said Blazer. “The question remains if the risk factors causing the tumors on these older fish, could also be harming the younger fish in other ways, such as early mortality or lack of reproduction. We really don’t know right now.”

Another unknown is the cause of these tumors.

Blazer said there are some studies that suggest exposure to certain chemicals can cause liver tumors in fish, but there is still more research needed to determine the exact cause. 

“The fact of the matter is that tumors in fish, just like tumors in humans, are multifactorial and we really need more research to identify what the risk factors behind these tumors are,” said Blazer.

Several sediment cleanup projects to remove legacy contaminants from AOCs have been completed in Sheboygan and Milwaukee since the time the USGS study was initiated, and additional sediment cleanup projects are underway in Milwaukee. The Wisconsin Department of Natural Resources anticipates that additional studies will be needed to monitor the levels of liver tumors as AOC recovery occurs over time.

For more information on this study – which was conducted in cooperation with the Wisconsin Department of Natural Resources and the University of Wisconsin, with funding by the Great Lakes Restoration Initiative – click here to read the complete report.


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Jhon Lawrence