NOAA study: Yellow perch quickly purge a harmful algal toxin 

Dec. 8, 2011

Contact: Linda Joy, 301-734-1165

Great Lakes perch lovers will find good news in a new NOAA study that shows yellow perch efficiently eliminate a harmful algal toxin from their tissues. The findings suggest that unless the fish are caught during a toxic algae bloom, eating them will not likely expose people to unsafe levels of the toxin known as microcystin.

Perch are one of the most popular fish caught by commercial and recreational fishers in the Great Lakes – and one of the most frequently consumed. In recent years, however, their habitat has experienced more frequent blooms of microcystin-producing algae, typically from July through September. 

When humans consume contaminated food or water, microcystin can cause liver damage and gastrointestinal symptoms, such as vomiting, diarrhea, and stomach cramping. The World Health Organization recommends limits on a person’s daily intake of microcystin. Prior to going fishing, people can check with local authorities about harmful algal blooms in their lake.

The NOAA study found that perch fed a single dose of the toxin, similar to the quantity they would encounter during an algal bloom, eliminated most of it within 24 hours. The study, by scientists at NOAA’s Great Lakes Environmental Research Laboratory (GLERL) in Ann Arbor, Mich., and Wayne State University, was published today in the journal Marine Drugs. 

“Based on our data on the toxin concentration in yellow perch tissue, it looks like the fish are able to eliminate it very efficiently,” says Julianne Dyble, Ph.D., an aquatic biologist for GLERL and lead author of the study. “However, our study does not conclude that eating perch carries no risk for microcystin exposure or illness. There are still unanswered questions.”

What the scientists are certain about is that most of the toxin does not accumulate long term in perch muscle or liver. Their aim was to track how quickly yellow perch accumulated and eliminated microcystin from their tissues, particularly the muscle tissue, which is what most people typically consume.

In this study, scientists did not measure PCB or mercury levels in perch. The Michigan Division of Environmental Health ranks yellow perch as one of the safest Great Lakes fish for human consumption, but also recommends that women who are or may become pregnant and children limit yellow perch to one meal per week due to mercury and PCB levels in the fish. See the Michigan Fish Advisory for details, online at http://www.michigan.gov/documents/FishAdvisory03_67354_7.pdf.

In their two-part study, GLERL scientists first fed laboratory-raised fish a pellet of dry food spiked with microcystin toxin. By measuring the amount of the toxin in liver and muscle tissue at regular intervals over 10 days, the scientists determined that the fish excreted most of the toxin in the first 24 hours.

The second part of the study made a detailed analysis of the rates at which the toxin was accumulated and then eliminated from yellow perch liver and muscle tissue over the first 24 hours after the fish consumed a microcystin-spiked pellet. In both a high dose and low dose experiment, microcystin concentrations peaked first in the liver tissue, about eight to 10 hours after the fish ate the microcystin-spiked pellet, followed by a peak in the muscle tissue about 12 hours after the microcystin dose. 

To monitor the rise and fall of the toxin in the fish liver and muscle tissue, the scientists set up 48 fish tanks and put one perch in each tank. Each fish ate a single pellet containing a known amount of microcystin, and the scientists measured the amount of toxin in the liver and muscle tissue every four hours. 

In addition to measuring microcystin in the fish, the scientists tested the tank water to see how much of the toxin each fish excreted. After 24 hours, they found that the fish excreted 70 percent of the toxin they consumed in the low dose experiment and 59 percent in the high dose experiment. Only a tiny fraction of the toxin was measured in the fish livers and muscle after 24 hours. So, what happened to the rest of the toxin? 

“The problem with measuring microcystin in tissue is that you can’t get all of it back out,” Dyble explained. “Some of it gets bound to the tissue and can’t be measured using our current methods. What we have measured in this study is the unbound portion of the toxin.” Some of the toxin also may have passed into other fish organs, such as the heart or brain, which were not measured by Dyble and her team in this study. Scientists do not know whether the bound portion of the toxin can sicken people.

Microcystin toxin is a growing concern for Great Lakes fish lovers. Algal blooms that produce the toxin have been increasing globally, driven by nutrients from agricultural fertilizer and sewage that flow into lakes and coastal oceans around the world. In the Great Lakes, algal blooms typically occur from July through September. 

The NOAA Oceans and Human Health Initiative funded this study at the Center of Excellence for Great Lakes and Human Health at GLERL.

NOAA’s mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Visit us at www.noaa.gov and join us on Facebook, Twitter and our other social media channels.

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On the Web:

NOAA Research: www.oar.noaa.gov

Great Lakes Environmental Research Lab: http://www.glerl.noaa.gov

HABs GLERL: http://www.glerl.noaa.gov/res/Centers/HABS