This Tiny Fish Can Withstand Almost Anything

Originating in the Great Dismal Swamp of Virginia, just south of the Chesapeake Bay, the Elizabeth River is turbid and brackish, its banks redolent with the nose-wrinkling stench of rotting vegetation. These muddy, pungent waters support an array of life—oak and maple trees, herons, otters, and oysters. But the Elizabeth empties into the massive Norfolk Harbor, making it ideal for shipping and shipbuilding; for decades, local industry spilled thousands of tons of creosote, a wood preservative made from coal tar, into the river.

Over time, the stench of tar and mothballs replaced the natural Eau de Liz. When the Duke University toxicologist Richard Di Giulio first walked along the Elizabeth in the late 1990s, its waters were some of the most polluted in the country. By 2009, there were half a dozen Superfund sites within a mile of the river.

Below the iridescent slime covering much of the river’s surface, though, a greenish minnow-size baitfish called the mummichog—also known as the Atlantic killifish—was managing to eke out a living in the waters that abut the Elizabeth’s Superfund sites. For Di Giulio and others, the mummichog is a case study in the costs of survival: The fish have managed to endure in the river, but some have undergone fundamental genetic changes.

For the humans who continue to live along the Elizabeth’s shores, mummichogs raise uncomfortable questions. A 1990 study discovered that one-third of the mummichogs from a notoriously polluted site had liver cancer, and more than 90 percent had precancerous lesions—rates that declined precipitously following cleanup efforts. Some residents wonder: If the chemicals in the Elizabeth have done all that damage to the fish, what are they doing to us?

By the time Lindsay Jasperse and Melissa Chernick pulled up to the chain-link fence surrounding the former Atlantic Wood Industries site, the late-July sun was already high in the sky. The researchers had left Di Giulio’s lab in Durham, North Carolina, before dawn, charged with bringing back a new batch of mummichogs for the lab’s experiments, and despite the heat they got right to work. Wearing masks and waders, they tossed a succession of stainless-steel minnow traps into the Elizabeth. Mummichog researchers used to bait the traps with high-end fish food, but then someone—no one remembers who—figured out that what the fish really like is cheap, store-brand hot dogs.

“They just love them,” Chernick told me.

After anchoring their string of traps to a low-hanging branch, Jasperse and Chernick beat a quick retreat to their air-conditioned car and drove to another site to repeat the ritual. Each site is distinguished by a slightly different toxic stew, and because mummichogs only travel 300 to 500 meters from their birthplace during their lifetime, the researchers know that the fish they collect have only been exposed to the chemicals at their capture location. Through close study of the mummies at each site, the team hopes to better understand how the pollutants influence living systems.

“Unlike most coastal fish, if you catch a killifish and see something about it—it has cancer or whatever—you can pretty well take it to the bank that it is due to something where you caught it,” Di Giulio told me. “The fish didn’t bring it in from New Jersey.”

After two hours, Jasperse and Chernick returned to their starting point and hauled in their traps. The first was mostly empty. The next trap, however, was filled with dozens of mummichogs—a mass of mottled olive backs and pale bellies, flashing in the sun as the fish struggled to escape.

The researchers emptied the trap into a large bucket of water and began sorting the fish by size and sex: Larger mummies with round bellies are older and healthier than their smaller counterparts, making them more likely to produce lots of eggs or sperm back in the lab. Those were gently placed in a large cooler for the four-hour drive back to Durham; the smaller fish were returned to the river. As Chernick and Jasperse bent over the bucket, their waders puddled around their feet to relieve the oppressive heat, a passerby gave a shout.

“Y’all catchin’ crawfish?” he hollered.

Jasperse shook her head. “Mummichog!” she called back.

The man raised an eyebrow beneath his tattered baseball cap. “That’s a lot of bother for some bait,” he said.

While Jasperse and Chernick finished sorting their catch, they explained that specific sites on the river had high levels of pollution that would have likely killed most species of fish, and that they were trying to figure out why this one had survived. The man nodded at this explanation and walked away; inquisitive passersby are rare, but the researchers are used to answering the most common questions:

Are the sites being cleaned up? Some have, and others will be.

Does the creosote harm the fish? Yes, the chemicals are hard on their livers, and might cause longer-term problems, too.

Will the pollution cause similar problems in humans? Scientists aren’t sure. Though creosote contains substances that are carcinogenic in both fish and humans, it’s unclear what the developmental effects observed in fish might mean for us. But mummichogs do give toxicologists like Di Giulio an opportunity to understand if and how organisms can adapt to heavily polluted environments.

The mummichog’s remarkable survival abilities were first recognized in the early 1970s, when the marine ecologist Judith S. Weis and her husband, Peddrick, decided to use the species to investigate the effects of the toxic chemical methylmercury on marine life. They collected mummichogs in Montauk, an unpolluted spot at the tip of Long Island. Back in the lab, the couple spawned them and raised the embryos in water containing methylmercury. The eyes of some embryos, they found, were closer together than usual; a few were so close that they formed a single cyclopic eye. Many also had heart and skeletal problems. But a few appeared to be completely unscathed by their noxious surroundings. And when the couple later performed the same experiments on fish from a polluted area in New Jersey, the embryos were nearly all resistant.

Elsewhere along the Eastern Seaboard, scientists found other mummichog populations that could tolerate staggering pollution levels. Some researchers worried that their persistence provided ammunition to those who argued against cleanup: If these fish could survive, perhaps the pollution wasn’t that bad. But when Wolfgang Vogelbein, an animal pathologist at the Virginia Institute of Marine Science, or VIMS, anesthetized some mummichogs from the Elizabeth and filleted them open, he found that their livers were mottled and visibly enlarged. Their surfaces were covered in nodules and bumps, as if the organs had a bad case of acne. In total, Vogelbein found that 93 percent of the mummies near Atlantic Wood had liver problems, and one-third had cancer. Other studies found that mummies living near industrial sites in New York, Boston, and Los Angeles also had elevated rates of liver problems.

“Fish like the mummichog—these fish are smoking four packs of cigarettes a day, and they can’t quit,” says Michael Unger, an environmental chemist and a colleague of Vogelbein’s at VIMS. “Their environment is contaminated. And we’re all exposed to these compounds daily. They’re everywhere.”

Di Giulio first heard about the mummichog work being done by scientists at VIMS about 25 years ago, as a freshly minted Ph.D. toxicologist at Duke. He learned that when researchers placed mummichog embryos from the unpolluted waters of the York River—50 miles north of Norfolk, Virginia—into aquariums with sediment from the Atlantic Wood site, all the fish died. But when the Atlantic Wood offspring were raised in clean laboratory water, those fish also struggled. In order to survive in the Elizabeth, it seemed, the population had reduced its ability to live in clean water.

Mummies in polluted sites along the Elizabeth River and elsewhere on the Atlantic and Gulf Coasts had somehow found a way to tolerate highly polluted water. What Di Giulio wanted to know was whether the fish had just acclimated to the pollution or had evolved a tolerance for it.

The difference is important: If you or I were to travel to a Mount Everest base camp, we would initially struggle to breathe in the oxygen-depleted air, but our bodies would start to produce more red blood cells to help us cope in that environment. Once we returned to sea level, our bodies would return to normal. That’s acclimation. Some of the Indigenous peoples who live high in the Himalayas, however, have inherited genetic adaptations that let their bodies make more efficient use of scarce oxygen. If they were to travel to Virginia, they would have the same physiology, no matter how long they stayed. This is what scientists call adaptation.

With his colleague Joel Meyer, Di Giulio collected some Elizabeth River mummichogs and raised several generations of them in large aquariums filled with clean water and mud. Despite their lack of exposure to the river’s contaminants, these subsequent generations of Atlantic Wood fish continued to show increased resistance to the birth defects elicited by these compounds when placed back in dirty water to breed compared to control-site fish. Whatever enabled the mummichogs to survive in the Elizabeth was clearly heritable—a sign that the fish had genetically adapted to the pollution.

“It was like they were actually better off, at least in the short term, in the presence of these pollutants,” Meyer says. But it came with a price. While the Elizabeth River mummichogs might have figured out how to survive these toxicants, they died after less than 90 minutes when exposed to a compound that became toxic when the fish were placed in direct sunlight—an hour sooner than the York River mummies. In the cloudy waters of the Elizabeth, with limited UV penetration, this wasn’t an imminent problem, but it was worrying nonetheless.

In recent years, new genetic tools have allowed scientists to ask questions about the fish’s ability to withstand pollution, however poorly, at the DNA level.

“How are these killifish doing this?” asks Andrew Whitehead of the University of California at Davis. “How did they get from this sensitive little fish to this super-resistant fish in, you know, a few dozen generations?” To find answers, he sequenced the mummichog genome, comparing genome sequences of 384 mummichogs from non-polluted sites with those from four highly polluted areas, including the Elizabeth River. All the mummichogs from polluted sites exhibited modifications in genes that code for proteins that help regulate the detoxification of chemicals such as polycyclic-aromatic hydrocarbons, polychlorinated biphenyls, and many other harmful chemicals. Whitehead concluded that only mummichogs with variations in these genes can survive in tainted waters.

A follow-up study revealed that the species has a tremendous reservoir of genetic diversity, making it more likely that at least a handful of fish were naturally more able to tough it out in toxic watersheds and live long enough to pass on their genes. And while it didn’t prepare them to cope with pollutants, the fish also had to tolerate changes in salinity and temperature, since they lived in shallow, tidal waters, Di Giulio explained.

“They’re a tough fish,” he said. When the rare mummie escapes from its tank, it can survive on the dry floor for a while before being rescued. Other species would have been long dead, but the mummichog is no worse for wear.

The irony is that scientists know far more about the effects of the Elizabeth’s pollution on mummichogs than about the river’s impact on its tens of thousands of human neighbors. As Di Giulio and other biologists unraveled how the mummichog adapts to poisoned waters, a few residents of Norfolk and the nearby city of Portsmouth were asking how the same chemicals were affecting their families.

As she does most afternoons now, Pat Burns sat outside her Portsmouth home on a rickety folding chair with a basket of old fabric. While her granddaughter played with Tonka trucks on the sidewalk, Burns crocheted together rags, draping the rug in progress over her lap. For someone who has spent most of her adult life as an activist, these quiet afternoons are a novelty.

Since leaving Jamaica and immigrating to the U.S. in her early 20s, Burns has lived near the Elizabeth’s polluted waters. When she moved to Portsmouth in 1989, she could often smell the river before she saw it.

“It was awful,” she told me, with a shake of her long gray braids. “I just … I can’t even describe it.”

Everyone knew that the Elizabeth was polluted, but it didn’t stop Burns’s neighbors from fishing in the river and eating their catch. Free food was hard to pass up, Burns said, especially with few grocery stores within walking distance.

As an activist, Burns often spoke at city-council meetings on issues ranging from public housing to education to mass transit, and she noticed that the pollution in the Elizabeth River never seemed to appear on the agenda. Burns had long suspected that the smell she endured as a young woman meant that health threats were lurking below the river’s surface.

She has plenty of nearby beaches to visit, but that’s not the point, she said: “I shouldn’t have to go to the reservoir to go fishing. I should be able to go right downtown. I should be able to jet-ski from right here.”

Few other locals spoke up about the pollution until Marjorie Mayfield Jackson, a local newspaper reporter, left her job to found the nonprofit Elizabeth River Project in 1991. Unlike Burns, the ERP had enough connections and social influence to convince corporations to clean up their act. Early on, Burns helped plant sedges and marsh grasses as part of an ERP-led restoration of Paradise Creek, a tributary of the Elizabeth River that winds through Portsmouth. The ERP has also built dozens of oyster reefs, which are designed to filter the river’s water.

Many of these projects have been organized by Joe Rieger, who has worked with the ERP for the past 18 years. I first met Rieger not far from the former Atlantic Wood site where Chernick and Jasperse baited their traps. Our brief introductions on the side of the road were drowned out by the deafening rumble of dump trucks and tractor trailers driving to and from the nearby industrial sites. Motioning me away from the racket, Rieger led me between a chain-link fence and a dense stand of phragmites. Gesturing at an expanse of bare grass the size of several football fields and dotted with squat cement fuel silos, he welcomed me to Money Point, a crescent of land along a bend in the southern branch of the Elizabeth River.

The ERP began working on a cleanup of this site in 2006, eventually carting away 39 million pounds of toxic sludge. After removing or capping the creosote-laden sediment, ERP contractors installed an oyster reef. With funds from local industry and the Environmental Protection Agency, Rieger and the ERP then planted five and a half acres with native flora. After more than a decade of work, polycyclic-aromatic hydrocarbon levels at Money Point have dropped from some of the highest in the region to levels similar to nearby unpolluted areas.

Rieger led me up a small rise covered in marsh grass, dogwoods, flowering asters, and other native plants. The leaves of a holly tree tugged at his blue chinos as we picked our way through the brambles and down the other side of the berm. A hundred feet in front of us were the muddy waters of the Elizabeth, ambling toward the Atlantic.

For the ERP, the Money Point project is a shining star. But for the area’s few remaining residents, the restoration isn’t nearly enough.

In the 1980s, construction of Interstate 464 divided Money Point and the South Hill neighborhood from the rest of South Norfolk. The city rezoned the area west of the highway as industrial, leaving its residents physically and financially stranded. Due to this rezoning, new houses and additions can’t be built. The residents can’t sell their property, either, since no one will move in. These homeowners, Rieger observed, are no more mobile than the mummichogs.

We knocked on several doors to see if residents would talk about their experiences. No one answered, their doors locked tight against noise, pollution, pandemics, and reporters. South Hill was a thriving neighborhood, Rieger said, until pollution and rezoning starved its life force.

Although no new creosote pollution threatens the river and those who live alongside it, other projects do. Several years ago, Virginia Natural Gas announced the construction of the Southside Connector pipeline. The connector became operational in 2019, linking the region’s existing supply lines and crossing under the Elizabeth River on its eight-mile journey.

The community activist Kim Sudderth worried that the pipeline would not only pose a direct safety threat—its route passed close to an elementary school—but would also imperil the river’s recovery. As the Virginia manager for Mothers Out Front, a group working to fight climate change and environmental racism at the local level, Sudderth knew that low-lying Norfolk’s chronic flooding problem was getting worse because of climate change, and that the floods were already bringing pollution with them.

“Knowing that the water is contaminated—it’s that threat multiplier,” she told me. Flooding could damage her car, or even her home. “And now I might get this awful skin infection through the water,” she says.

Sudderth said she doesn’t need a cancer-ridden bait fish to know that the waters aren’t healthy, but neither she nor anyone else knows much about the specific health threats the pollutants pose. VIMS is funding a community-based environmental-health study in which an interdisciplinary team of scientists—including mummichog researchers—will engage with community members such as Burns and Sudderth, documenting their river-related health concerns and laying the groundwork for a formal study of the pollution’s effects on human health.

It’s the type of work that Diane Nacci, a research scientist at the EPA, has often contemplated in her nearly 30 years of mummichog research. The clues contained in the fish, she told me, provide “a real unique opportunity and a really interesting way to try to estimate how these contaminants might affect human beings.”

For Burns, the community-health study is a huge relief. She has been worrying about the dangers posed by the river’s pollution for nearly half a century; that someone is finally investigating her concerns, even by way of a common bait fish, means that she might one day get some answers.

“Every time I hear about something else that’s positive, I get really excited, because there’s a possibility of the future being better,” she said.

With the mummichogs that Jasperse and Chernick captured this summer, Di Giulio’s lab is studying some of the more subtle impacts of polycyclic-aromatic hydrocarbons and other pollutants. Jasperse has found preliminary evidence that long-term creosote exposure alters mummichog behavior; the team is also beginning to perform direct studies on mummichog brains. Whether the Elizabeth’s creosote-laden waters have similar impacts on humans isn’t clear, but the studies underscore that just because mummichogs have evolved to survive doesn’t mean they’re unscathed by their toxic lifestyle.

Now that the EPA has begun cleaning up some of the area’s Superfund sites, toxicologists have documented a sixfold drop in liver cancer in mummichogs trapped at Money Point. Yet when Di Giulio analyzed the genomes of fish caught at Money Point in 2019, they hadn’t reverted to their pre-polluted state. Persistent creosote exposure was still writ large in their DNA. And none of the fish that Jasperse and Chernick collected in the past two summers showed signs of regaining their species’ original physiology. “It’s going to probably take awhile for these fish to re-evolve and then go back to the wild type,” Di Giulio said. But if the river stays clean, they eventually should.

Standing near the edge of the Elizabeth at Harbor Park, where the river’s eastern and southern branches converge before traveling on to the Atlantic, Sudderth and I discussed the outlook for humans living near the river. As we chatted, a pale heron glided in on ghostly wings, landing silently on the decaying timbers of an ancient pier. It glanced at the two brightly clad bipeds standing on the grass, then disappeared behind a collapsed pylon. The Elizabeth might yet return to her former fetid glory—if all her species can get a chance to heal.