Invasive species are among the foremost threats to biodiversity.

They can take over an ecosystem because there are no biological controls to keep their numbers down. And can even drive native species to extinction and undermine the normal functioning of the ecosystem.

It’s not just the environment they affect either. Invasive fish, insects, and plants can also inflict massive economic losses to fisheries, agriculture, and forestry. Once entrenched, invasive species are almost impossible to eradicate.

China is one of the world’s worst affected countries. Hundreds of non-native species — plants, insects, fish, molluscs, reptiles, and amphibians — have found their way into its forests, grasslands, lakes, and rivers.

While the exact number of invasive species in the country is still undetermined, scientists have only recently started to estimate the harm done to China’s ecosystems.

Some invasives may even try to eat your pet.

One July afternoon 10 years ago, a Guangxi local in South China was bathing his dog in the Liu River when it was attacked by three ferocious fish. The pet’s owner grabbed one fish, which promptly bit a chunk of flesh from his palm.

He, however, managed to throw the fish onto the river bank and then carried it home. An online search identified the predators as red-bellied piranhas. The fate of the dog remains unknown.

Red bellied piranhas normally inhabit the rivers of South America. The incident, reported in local media, was questioned by specialists, since piranhas are not nearly as aggressive as Hollywood movies portray them to be.

But such attacks are not that far-fetched either.

Aquariums around the world keep piranhas. Fast-growing, the carnivorous fish often quickly become too big for their tank and there have been many instances in Europe and the U.S. of owners dumping unwanted piranhas into the nearest river or lake. With a similar climate and conditions as South America, Southern China offers piranhas a good chance of settling in as invasive species.

China’s official register of wailai wuzhong, or invasive species, is compiled by six different government departments, including the Ministry of Ecology and Environment and the General Administration of Customs. The list currently has just 59 entries — mainly plants — but biologists have long called for its urgent expansion. Data show that hundreds of species, from alligator snapping turtles and electric ants to Amazonian giant snails and Canada geese, are invasive in China.

There are several reasons for such a variety of invasive species in the country.

China’s range of climates and ecosystems accommodates newcomers from both bitterly-cold, snow-covered Siberia and the tropical and humid Amazon.

And since China is a trading powerhouse, new species, especially insects and plants, arrive at its shores from every corner of the globe, often stowing away amid the cargo. Others are brought in as stock for China’s vast fish, frog, shrimp, and turtle farms from which they escape.

Moreover, the demand for pets, particularly the exotic, has surged in China. In 2019, the pet market was valued at over 200 billion yuan ($29 billion). As demand grows, more and more diverse species are brought in. Many invasive species entered the ecosystem when they were discarded, escaped, or were deliberately released.

Some species have been introduced by design in an attempt to “improve” nature by providing local fishermen with faster growing fish, or farmers with natural tools to control pests.

Among the earliest examples of foreign species arriving in China was the tamarind tree, brought from India to Yunnan in 4 B.C. Two centuries later, pomegranate, safflower and alfalfa were brought via trade routes from Central Asia, and spread quickly in western China. In the 1600s, American species started to arrive, such as the prickly pear cactus which is now common across south China.

But it was in the 1980s, after China’s economy opened up, that more and more invasive species streamed in. And fish were at the front of the line.

Benign beginning

Aquaculture — farming fish, shrimp, and shellfish — has boomed ever since the Chinese economy was liberalized. China now accounts for almost half the world’s aquaculture production.

Most of the now-invasive species of fish came as stock for China’s vast fish farms. Species like the Mississippi paddlefish, Eurasian eel, Nile tilapia, South American peacock-eyed bass, Asian walking catfish, and many others managed to escape or were deliberately released.

Almost 20 million people in China had aquaria in 2019, and the country is now one of the world’s biggest importers of ornamental fish. Dozens of non-native species that now live in the wild in China, such as the green swordtail fish, three-spotted gourami, as well as various catfish, were initially brought in as imports.

Other species were introduced deliberately. The rainbow trout and European perch were released in western and northern China to improve local fish stocks.

Scientists put the number of non-native fish species recorded in the wild in China at over 500. Self-sustaining, breeding populations of about 70 such species have been confirmed, but there are likely many more.

In the southern Guangdong province, China’s aquaculture hub, the climate resembles that of both South America and South East Asia — regions from where many aquarium and aquaculture species originate. Unsurprisingly, Guangdong also harbors the most invasive fish species among all provinces — 160 non-native fish species have been detected in its lakes, rivers, and canals.

Guangdong’s rivers are now full of the South American suckermouth catfish. Known as plecos, they clean aquaria by attaching themselves onto the glass and grazing off algae.

Plecos are inedible and have no commercial value. Hardy and armored, they have thrived in Guangdong’s waterways and pushed out shrimp and local fish species that are important for fishermen, whose catch, and income, have dropped.

This species also illustrates the fragility of nature. Compared to native fish, plecos excrete less phosphorus, reducing its availability to plants and thus undermining the stability of the ecosystem.

Also raised on fish farms in South China are billions of African tilapias. They are now the main predators in some of Guangdong’s rivers and lakes, consuming all the wildlife they can. Tilapias also excrete large quantities of nitrogen and phosphorus which creates algal blooms and ruins water quality.

Some invasive fish are just plain intimidating.

In 2022, a large and vicious-looking species called the alligator gar terrified locals and authorities in at least three provinces following a spate of sightings. Native to North America, alligator gars, which have razor-sharp teeth and can grow to over two meters in length, are sold online as pets for as little as 20 yuan ($3).

Entire lakes were drained to capture the gars amid a media frenzy. The incident brought much-needed attention to the problems that invasive species pose.

Small but deadly

Another invasive species that made headlines in 2022 were electric ants.

Originally from South America, these tiny ants — no larger than 2mm — can cause enormous damage. Able to utilize various sources of food, electric ants can thrive in almost any environment in tropical and subtropical climates. They outcompete, or even eat, native ants, devour other insects and spiders, attack and eat larger animals, and inflict painful stings on farmers.

Their larger invasive cousins, red fire ants, are already present in about a dozen provinces and electric ants are likely to follow suit.

Turtle power

For thousands of years, China has farmed turtles for food and medicine. The industry exploded in the 1990s and is now worth billions of dollars per year. Hundreds of millions of turtles are produced annually.

Globalization has brought turtles from across the world for Chinese breeders to work with. And more than 100 species of turtles are now farmed in China for food, medicine, and for the pet trade.

Four of the most commonly imported and farmed turtle species — the red-eared sliders, alligator snapping turtles, common snapping turtles, and Florida softshell turtles — have been confirmed as invasive, but the true number of invasive turtle species is likely to be much higher.

Meanwhile, almost all native Chinese turtles are endangered, many critically. Considering the sheer scale of the influx of foreign turtles into China, there is a real danger that invasives may eventually replace many native turtle species.

Genetic damage

Invasives can also undermine biodiversity by interbreeding with native species.

Sturgeons are amongst the last surviving freshwater megafauna. All species of sturgeon are now critically endangered, having been fished to near extinction for meat and caviar, and their habitats destroyed by river damming and pollution.

In China, there are several native species of sturgeon, all on the cusp of extinction. China is also the world leader in sturgeon farming, and both native and not-native species are raised for their meat and caviar. The loosely regulated industry, however, has created a variety of hybrids.

According to the specialists, after years of uncontrolled and rampant cross-breeding, a lot of the sturgeon stock on China’s farms is now of blurry genetic origin that may include both native and non-native species of sturgeon. This poses a threat to China’s remaining wild sturgeon.

Baby sturgeons are now sold on animal markets as pets for as little as 20 yuan, and it is likely that some are hybrids. If they find their way into the habitat of native wild sturgeon, the two can interbreed, changing the genetics of the native species with unforeseeable consequences.

Way forward

While more and more non-native species are slipping into China, the issue of invasive species is finally being addressed.

In 2022, China passed a new biosecurity law, which classified the introduction of non-native species as a criminal offense. Experts hailed the move as a big step forward.

The public, too, is now more aware about the issue, primarily thanks to the recent sightings of the ferocious-looking alligator gar and snapping turtles reported widely in the media.

There have also been increased restrictions on fangsheng — the Buddhist practice of setting animals free to gain good karma. To help the public, a list of invasive aquatic species whose release is prohibited, has been published.

The list includes red-bellied piranhas, the species that attacked the pet dog in Guangxi in 2012.

Editor: Apurva; Visual editor: Ding Yining.

(Header image: Luo Yahan and Ding Yining/Sixth Tone)