New Research Advances Efforts to Combat Invasive Silver Carp

Study makes it easier to identify invasive carp eggs and larvae in water samples.

Invasive species can be disastrous for local ecosystems, and the invasive silver carp (Hypophthalmichthys molitrix) is no exception. The fish, which is native to eastern Asia, was introduced to the United States in the 1970s after escaping from aquaculture operations in the South. It has since spread up the Mississippi River, and now poses a risk of entering and establishing itself in the Great Lakes.

Knowing how dangerous a Great Lakes invasion of silver carp could be, a new study published in PLOS ONE provides key genetic information for these fish, allowing resource managers to more effectively monitor water samples for silver carp. The research was led by Carol Stepien, Ocean Environment Research Division leader at NOAA’s Pacific Marine Environmental Laboratory. We sat down with Carol to learn more about the silver carp and how her new research helps in the effort to track and control it. 

Why did you choose to focus on silver carp?

I believe that silver carp is the species that’s currently presenting some of the most considerable harm to the future of American freshwater ecosystems.

Why is that? What sorts of impacts do silver carp have on the ecosystem?

They’re very prolific, they grow to a very large size, and they eat very low on the food chain — so they eat a lot of other fish’s food. And they’re right on the gateway of the Great Lakes. They escaped from catfish rearing farms in Alabama and Mississippi, where they were brought over from Asia to clean up algae back in the 1960s and 1970s, and they’ve been reproducing and moving up the Mississippi River ecosystem ever since. They’re very gregarious and there are lots of them — they’re the fish that jump out of the water when they hear boat vibrations, and hit people in the face.

They’re considered a delicacy in Asia, where they are purchased live, but they’re not as popular here where they are sold as frozen fish. However, Illinois and some other states are trying to develop a market for them as frozen fillets and cat food. 

What did you set out to find in this research?

My laboratory group conducted a population genetics analysis across the silver carp’s range in North America, including at two fronts through which they are likely to enter the Great Lakes — in the Illinois River outside Chicago, and the Wabash River in Fort Wayne, Indiana, which floods into the Maumee River, which then would enter Lake Erie.

We found there was ancient introgression — which is hybridization — with the large scale silver carp, a separate Asian species that’s very poorly studied. We found that about 6 percent of our silver carp had this hybridized DNA. We developed a genetic marker to be able to distinguish and identify silver carp and other invasive carps as eggs and larvae, because one of the problems with identifying them is that when they’re little they look alike, and like every other minnow. 

How does this research help advance our understanding of silver carp, and of invasive species in general?

This study is the most comprehensive analysis of the population genetics underlying the silver carp invasion and expansion in North America. This is a species that has considerable genetic diversity — which is bad for us. It means it’s hard to defeat as an invader, as it’s very adaptable. But with this new genetic marker, we are able to distinguish all types of carps, including invasive ones and native species. We can find out by testing a liter of water if they’re in the water body. 

One of the best ways to check them early on is from plankton tows. It’s easier to control invasive species earlier rather than later — we may be able to cull them from the water by fishing them out or combating their early life stages. It’s important to encourage research that uses sequencing like this so that we can use new technology to detect and combat invasive species. 

What’s next in terms of this research? 

We’ve developed diagnostic genetic markers for a wide variety of different invasive species in the Great Lakes, and I have some new research at NOAA’s Great Lakes Environmental Research Laboratory that is designing and implementing markers in NOAA sampling across the Great Lakes. 

Is there anything you’d like the public to know about these fish?

Raising people’s awareness of invasive species is very important. The Great Lakes has 187 non-native species that have become established, and invasive species, next to habitat loss and destruction, are the greatest threat to worldwide biodiversity. 

In the case of silver carp, we’ve found that it is actually mixed in with bait species for sale. So, if you fish and buy bait, don’t move bait around. Buy it near where you fish, so that you don’t move it from one ecosystem to another. And dispose of it in your nearest trash container — don’t release it live.