LAS PEÑITAS, Bolivia—Before he’d ever seen a paiche, fish trader Eric Salazar had heard the giant Amazonian fish could grow up to 10 feet long, weigh 400 pounds and eat a man whole. The paiche, or Arapaima gigas, is the world’s largest scaled freshwater fish. Native to the jungles of Peru and Brazil, it first appeared in nets in Bolivia’s Amazon Basin in the early 1990s. As it migrated upriver, rumors traveled with it. People said it was created by nefarious Peruvian scientists, that they fed it with the blood of farm animals, that it wasn’t a fish at all but a monster.

They weren’t entirely wrong. The paiche is carnivorous—although it eats other fishes, not humans. And it did enter Bolivia from Peru, where it had been added to the Convention on International Trade in Endangered Species index in 1975 as a species prone to extinction if trade was not closely controlled. A few years later a flood washed juveniles out of a Peruvian fish farm near the border into Bolivia’s watershed. By the time Bolivian fishermen noticed the strange creature, it was already established in the oxbow lakes and seasonal lagoons that dot the forest.

Since then the paiche has spread across more than 340 square kilometers, roughly a quarter of the Bolivian Amazon. There are no official data yet on its impact but there’s plenty of anecdotal evidence of environmental damage. Fishermen who’ve worked these waters for years say the native species they prefer to eat—particularly giant Amazonian catfish like surubí, bagre and pintado—have become scarce. Others, they say, have disappeared entirely.

In the last decade paiche meat has also become more popular among city dwellers. Conservation-minded chefs in the cities promote paiche as a sustainable choice, which is true at face value: The fish is a nuisance and other edible river fishes are disappearing. The idea is to control or maybe even eradicate the fish by deliberately overfishing it, but Salazar, who profits handsomely from the paiche’s lean, white meat, says that would be impossible. “To eradicate the paiche,” he says, “would be to pull a star from the sky.”

Bolivia is now faced with a controversy that, for the last decade, has been a central debate in the young field of invasion ecology here in U.S.: Could human hunger help control the spread of invasive species or will the rules of capitalism, combined with our unquenchable thirst for more, only make matters worse?

Eat Them to Death

An invasive is any species introduced by human intervention that has caused economic or ecological damage by growing superabundant in a nonnative habitat. Invasives can be fish, bivalves, mammals or plants. They can be as sinister as kudzu (“the plant that ate the South”) or innocuous as dandelions. They can be as delicious as wild boar; as unappetizing as the parasitic sea lamprey sucking blood from native fishes in the Great Lakes (they’re a delicacy in England); or entirely inedible, like the tiny zebra mussels clogging pipes and choking native shellfish throughout the upper Midwest.

Invasive species have followed us around the globe for as long as we’ve been mobile. They’ve hitched on the hulls of transoceanic ships, and we’ve carried them home with us deliberately, introducing them for food, farming and recreation. Invaders are now the second-most important cause of global biodiversity loss after habitat destruction, and the more we move about, the more they spread. Conservative estimates have invasives costing the U.S. tens of billions of dollars annually.

Among the first scientists to promote gastronomy as a tool to combat invasion was Joe Roman, a conservation ecologist at the University of Vermont. His 2004 article for Audubon, titled “Eat the Invaders,” articulated a simple argument: If we can hunt native species to extinction, as we have for eons, why not deploy our insatiable appetites against invaders?

Roman’s modest proposal had little impact when it first appeared. But as interest in food ethics, locavorism and foraging grew, the elegant logic of “invasivorism” hit a cultural sweet spot. In 2005 Chef Bun Lai created an invasive species menu for his sushi restaurant, Miya’s, in New Haven, Conn. In 2010 the National Oceanic and Atmospheric Administration launched its “Eat Lionfish” campaign to combat the species’s invasion of the Caribbean. In 2011 Food & Water Watch hosted an invasive species banquet at James Beard House in New York City. In 2012 Illinois extracted 22,000 metric tons of invasive Asian carp and sold it to China, where it is commonly eaten, for $20 million.

Other projects have taken a more participatory approach: The University of Oregon’s Institute for Applied Ecology hosts an annual Invasive Species Cook-Off (aka Eradication by Mastication); Web sites like invasivore.org—run by Matthew Barnes, a biologist at Texas Tech University—and Roman’s own site, EatTheInvaders.org, promote home recipes for exotic species. Even Whole Foods has gotten onboard; in 2016 the upscale grocer added lionfish to the shelves and started promoting it as “an invasive species” in the Atlantic Ocean and Caribbean Sea, “far from its native waters.”

Activism Outruns Data

But popular invasivorism has also preceded solid scientific study. “I don’t think we have the data yet to know if this is successful,” Barnes says. “There are a lot of small experiments going on but no large-scale data gathering.” What data does exist is less than conclusive. In 2013 a group of researchers from the Netherlands working on the southern Caribbean islands of Bonaire and Curaçao found lionfish biomass was 2.76 times lower in areas of Bonaire where harvest was encouraged than in areas where it wasn’t, and 4.14 times lower than in the waters surrounding Curaçao, where the local government has yet to begin control efforts by harvesting. Those numbers were promising. Yet in 2016 Fisheries and Oceans Canada wrote in a report there was an “extreme” risk of Asian carp species establishing populations in three of the five great lakes within 50 years, despite millions of dollars spent by the U.S. government to build aquatic barriers and promote harvest programs. Marketing aside, most people still find the fish unappetizing.

Invasivorism can also overlook some of the complexities of ecological invasion. Different types of invasives present different problems. Picking the leaves or fruits from plants like dandelions and Himalayan blackberries does nothing to keep them from growing. Telling people they should eat Asian carp won’t make the animal appealing. And even if you couldconvince people to eat nutria—the South American swamp rat introduced in the 1960s to clear Louisiana’s Mississippi Delta waterways of another invasive species, water hyacinth—there’s no way they’d be able to catch up with the population, which has already wiped out whole swaths of native greenery.

There is evidence that harvesting programs could be effective if started when the target population is still small and concentrated. In their cautiously optimistic paper for the U.S. Fish and Wildlife Service, biologists Susan Pasko and Jason Goldberg noted that between the years of 1981 and 1989 the U.K. successfully eradicated a nutria infestation by incentivizing trappers, although they don’t mention whether or not anyone ate the animals. Yet a similar program targeting invasive minks failed just a few years later because that animal had already dispersed too widely. “Incentive programs can only be successful,” the authors wrote, “if the number of individuals harvested exceeds the number that would normally not survive during a single breeding cycle.” For Caribbean lionfish, that might require removing up to 65 percent of the species. With plants, those numbers are even higher.

Backfire: Evil Fishes Become Popular Fare

The worst-case scenario of invasivorism is not that it won’t work, rather it will make a troublesome species popular. Martin Nuñez, an ecologist at the University of Tennessee, has published several papers warning of perverse incentives to distribute economically valuable species more widely. “If you make money off a species,” Nuñez says, “then that’s an incentive to help it spread.” Consumption is one of the most powerful incentives of all. Even advocates of invasivorism like Roman and Barnes raise the same concern.

In Hawaii, for example, feral pigs run rampant. Descendants of Eurasian boars from Russia and introduced for sport hunting long ago, they cause substantial damage to indigenous habitats. But to eradicate them would also be to kill an important part of the island’s cultural lexicon, built around the practice of hunting and roasting the animals. Pasko and Goldberg point out it could also create new environmental problems. Feral pigs eat the flammable, invasive grasses that now cover large swaths of the islands; without them, fires could become more common and destroy more native habitat than the pigs do themselves. In the continental U.S. people continue to spread wild boars by introducing them as game. They now cause an estimated $1.5 billion of damage annually and, within 50 years, will have reached every county in the country.

The same has begun to happen with Bolivia’s paiche, and on a much shorter timescale. Paul Van Damme, a biologist working on a fisheries management program called Peces Para la Vida (Fish for Life) with the Bolivian organization Faunagua, has already seen a second wave of paiche invasion. “We thought it would take 50 or 60 years for the paiche to arrive in the upper Mamoré or Iténez,” he says, referring to Bolivia’s other two lowland river systems. “But the species is already there.” This second invasion had multiple origins, among them poorly managed fish farms in Brazil where the species is also native and also overfished. In a particular case, he says, “this one guy actually distributed the species to farmers all over the basin,” with promises of boom times for paiche meat ahead.

A fisherman just outside of Las Peñitas cleans a piranha, one of the few fish local people like to eat that has not been decimated by the paiche. Credit: Nadia Del Pozo and Felipe Luna

He wasn’t wrong; paiche doeshave commercial potential. In the U.S. Whole Foods started pushing farmed Peruvian paiche in 2014, touting its “great back story” as a threatened species “rescue[d]” by sustainable farming. The grocer plans to double its stock for 2017. Also in 2014 a widely publicized study out of Peru and Brazil found the paiche was extinct in 19 percent of the 80-plus communities surveyed and nearing extinction in 57 percent. The same study found farming had positively affected wild paiche populations by redirecting harvest pressures to farmed populations. But fish farms are also notoriously difficult to regulate and prone to accidental release: Asian carp in the Midwest (introduced to clean algae from the farms), Louisiana crayfish in China and Atlantic salmon in the southern Pacific have all done substantial environmental damage after escaping from fish farms. The same fish farms that “rescued” the paiche in Peru might also ultimately destroy Bolivia’s Amazon.

In the areas of Bolivia where the paiche first appeared about 25 years ago it now accounts for 90 percent of wild catch, although it is unclear whether that’s because other fish species are gone or because local fishermen have been successful in focusing on the invader. In places where the fish arrived more recently its growing market value has drawn more fishermen to the river, increasing pressure on paiche as well as native species. In other places, Van Damme says, paiche has become an alternative to blanquillo, a native species typically fished using freshwater dolphin meat as bait. In still others paiche has driven both local fishes and local communities away from the water entirely. Even a single invasive species in a single river system can have staggeringly diverse effects.

The goals of conservationists and activists are no less varied. Roxana Salas, who heads Faunagua’s legal arm, says her team is working to craft laws that promote economic growth via sustainable paiche fishing. Fish and Wildlife’s Goldberg describes “adapting to irreversible ecosystem changes” as “a means of last resort.” For Chef Bun Lai, invasivorism is a way of “shifting our appetites” away from the unsustainable species we currently favor. Barnes and Roman see it principally as an awareness campaign—“a way to get [invasives] on people’s radars,” as Roman says. They all agree that preventing invasives from arriving in the first place is the only real solution and that invasivorism will only be an effective management tool in cases where the culprit is caught early. “Invasivorism is not going to save the planet and it’s not going to solve all of our problems,” Roman says. “It’s a tool in the toolbox. But boy you gotta be careful.”

Tennessee’s Nuñez, for his part, is skeptical of the founding premise. “The idea is that if we can drive a native species to extinction by eating it, we could do the same with an invader—but it’s not obvious to me that those dynamics would be the same,” he says. “Something can be intuitive and also be wrong.”

In Las Peñitas the intuitive choice is to fish the new species away and restore the environment to its previous balance. But it doesn’t take much work to reveal the flaws in that solution. In the first place, no environment is static, and the notion of balance is, as Barnes notes, “a social construct, scientifically tough to defend.” Many local fishermen see paiche as a boon, a lucrative commodity in a region otherwise starved for resources. It is obviously preferable to preserve native species, but also imprudent to ignore the economic potential a species might bring to a poor region of South America. There are plenty of incentives for fishing paiche. The question is whether they will do more harm than good.

Managing invasive species is, in the end, principally a question of managing humans. As Salazar and the many other fishermen of Las Peñitas asked out loud, time and again, “Who knows which is the worse predator—the paiche or us?”