Predicting effects of contaminants on Michigan's fish populations

A three-year project led by MSU Department of Fisheries and Wildlife associate professor Cheryl Murphy is exploring ways to protect fish populations and the bodies of water they live in.

The Michigan Department of Natural Resources indicates that fishing is among the most popular outdoor recreational choices in the state, generating nearly $2.5 billion of economic impact annually through trip- and equipment-related expenditures. With more than 1 million licenses purchased each year, angler participation in Michigan ranks fifth in the United States.  

A three-year project led by Michigan State University (MSU) Department of Fisheries and Wildlife associate professor Cheryl Murphy is exploring ways to protect these fish populations and the bodies of water they live in. An expert in aquatic toxicology, Murphy is directing a team of researchers from several universities to examine the impacts of contaminants on fish populations.

“It’s relatively easy to measure effects of contaminants on individual fish at the cellular level, but we really want to predict outcomes for the whole population,” Murphy said. “We’re interested in how these effects translate across different scales and species because that will enable us to make predictions for populations and communities of fish — an outcome that could help regulatory decisions.

“For Michigan, this work will help us predict how these legacy contaminants such as PCBs and mercury, as well as emerging chemicals such as pharmaceuticals, are affecting native species.”

With funding from the Environmental Protection Agency’s Science To Achieve Results program, the researchers are evaluating the effects of methylmercury and PCBs — a long-lasting and common environmental contaminant now banned in the United States — on four fish species.

The group — which includes Michael Jones from MSU, Natalia Garcia- Reyero from Mississippi State University and Michael Carvan from the University of Wisconsin-Milwaukee — is studying larval zebrafish, fathead minnow, yellow perch and killifish because they are good models for many species living in Michigan waterways.

In the lab, larval fish are placed into one of three scenarios: exposure to no contaminants, exposure to a low dose of contaminant or exposure to a high dose of contaminant. Growth and essential survival behaviors such as rate of swimming, feeding and prey detection are measured over a period of days.

Preliminary results indicate that fish exposed to increasing concentrations of methylmercury travel more slowly, their visual reactive distance varies and feeding declines. Consequently, ability to escape predators and capture food is impaired over time in the presence of contaminants. In simulations, fish subjected to a high dose of contaminants have significantly decreased survival rates.

Garcia-Reyero, who specializes in genomics, is examining larval fish brains to see which genes are expressed when stressors are applied and how fish respond behaviorally. The researchers have found a correlation between alterations in behavior and the expression of particular genes. This can help to predict large-scale effects of contaminants on fish populations and inform conservationists about where to focus efforts to combat ecosystem contamination.

“Molecular perturbations are really an important piece to this research because the effects of contaminants are often subtle or sublethal,” Murphy said. “Although the fish may not die, there are genetic and physiological changes that occur. If we know what those changes are, and we know that these are good model species, we can predict changes to various fish populations or identify reasons why populations may have declined already from our molecular work. These molecular-level responses are much easier to measure than an entire population or community of fish.”

The group chose yellow perch because the population has been trending downward in Lake Michigan. They want to learn whether contaminants are contributing to that population decline, or if there is some evidence that there is a combination of stressors such as invasive species. In concert with this research project, a community of global scientists is working to collect information from several fish species and bodies of water, and spanning multiple levels of biological organization.

Using a multitude of new technologies — genomics and computational tools, for example — and collaborative data-sharing tools, scientists have created a global network for discussion and feedback.

“My role is really trying to create quantitative linkages among levels of biological organization using the data from these projects,” Murphy said. “The more data we share with one another, the better. Through these efforts, we can really understand how contaminants and other stressors affect fish species all over the country and the world.”

Some researchers are even making connections to human health. Neurobehavior models have cross-species applications, so researchers can potentially use them to predict human health consequences of environmental contaminants. Murphy said research projects such as these can have a profound impact. A greater understanding of how human activity influences the environment helps governments and agencies develop legislation to create healthier ecosystems and promote sustainability.

“The people of Michigan really value our Great Lakes resources in this state,” Murphy said. “It’s important to protect them so we can enjoy them for generations to come. Ultimately, we want policymakers to do what’s best for Michigan.”

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