Malaysia Peng Chang - On a recent Sunday morning, about a dozen fishing net men bypassed the garbage strewn bank of the Klan River outside the Malaysian capital Kuala Lumpur.

While investigating the river, these people threw their nets into contaminated water. The Nets quickly spread and sank quickly under the weight of the metal chain.

From where they stood on the bank, they began to pull into the net, already filled with dozens of squirming black catfish.

"You can't see other fish," said Mohamad Haziq A Rahman, head of Malaysia's Foreign Fish Hunter Squad.

None of the fish caught that morning was for sale in nearby markets or food stalls. The sole purpose of this expedition is to pick on suckermouth catfish, one of the growing invasive species that have dominated freshwater habitat throughout Southeast Asia in recent decades.

Once for commercial or hobby reasons, invaded fish not only threatens to separate native species from the food chains in Malaysia and elsewhere, but also spreads disease and causes great damage to the local environment.

Invasive fish is a problem in the world’s past, but experts say Malaysia’s large II locations are keenly aware of the problem.

"More than 80% of the rivers in the Kran Valley are invaded by foreign fish, which could lead to the extinction of indigenous aquatic organisms in the river," said Dr Kalithasan Kailasam, a river expert at the Malaysia-based Global Environment Centre.

"It grows in almost every other major river in Malaysia," said Kerasam, explaining how species such as suckermouth reproduce and survive quickly in dirty water, while local fish stay on the loss side.

In addition to suction cups, Malaysia's waterways are now threatened by species such as aggressive peacock bass, Javanese carp and red-tailed catfish, he said.

Although the full extent of the problem is unclear, Malaysia's fisheries sector conducted a four-year study until four years of study in 2024, with invasive species found in nearly 39 areas of nearly every state of the Malaysian Peninsula and Paint Island.

Shocked by threats, a small group of citizens united to fight the aquatic invaders.

Under Haziq, they are working to recover Malaysia's rivers at one time.

Invasive fish invasion

Citizen fish hunters’ pursuit for invasive species began with the country’s 199 lockdown, when former health care consultant Haziq turned to fish in a river near his house in central central Selangor. He found that every fish he caught was a fool breed, also known as "pleco" or "ikan bandaraya", which translates as the Malay "guard mermaid" and is favored by amateurs to keep the aquarium clean because the suckers use algae as algae, leftover food and dead fish.

The variety of Suckermouth is native to South America and has also been introduced to waterways in the United States, Bangladesh and Sri Lanka, usually after the owner pours them into rivers, canals, dams or dams because they pour them into rivers, canals, dams or after they are too large for water storage tanks to be poured into rivers, canals, dams or after they are released.

Due to its thick scaly skin, larger predators in Malaysia generally avoid Suckermouth and can grow to about half a meter (1.6 feet) in length.

As a bottom feeder, catfish are known to eat eggs from other species and destroy their nesting sites. Cat fish also burrow into the river bank to nest, causing them to erode and collapse, which is a serious environmental problem in the prone to occur in Malaysia, where the year-end monsoon winds bring heavy rain.

The Malaysian Central Bank said in 2024 that floods are the cause of 85% of natural disasters in the country, with a frequency increase since 2020.

Haziq, who is far from his favorite fish fishing, found that suckerfish roe can be used as a bait for other big fishes, made some money to sell eggs to other fishing enthusiasts. He also gained a following by putting his vulnerabilities on social media. Further research then led him to understand the threat posed by invasive species.

Harziq is starting to attract like-minded anglers, and in 2022 they decided to form a group hunting suckermouth, meeting in the river almost every week for waves.

Their public image and popularity are growing. The group's membership has now grown to over 1,000 and has a strong follower on social media.

“People keep asking how to join our group because we are studying ecosystems,” Haziq said.

Fish Hunter first focused on the rivers in Malaysia's Selangor and the capital Kuala Lumpur, winning nearly 31 tons of suction cups in 2024 alone. They also visited rivers in other states of Malaysia as their campaign expanded.

Dispose, for research, cooking and eating?

During a hunt on the Cran River earlier this year, Hazker and his comrades deployed to the bank of the river to perform missions to see how many fools they could catch on an outing.

But finding invasive fish can be tricky. Without ships, hunters must dabble in the fast moving polluted water on muddy river banks while navigating underwater debris, such as garbage on the riverbed.

Almost all of their catches are invasive, but occasionally, they do purify the locals.

"Haruan (Snakehead)!" Syuhaily Hasibullah, a 46-year-old former black-handed diver, shouted half the fish the size of his arm, and took half the fish out of a net with several suction cups.

He told Al Jazeera: "This is rare! There were many in the river once."

Haziq said that if hunters spot many invasive species in the net, they would organize another outing at the same location and bring more people to participate.

The day they set out to figure out how many invasive fish they could catch a single outing, producing half a ton of suckermouth in just three hours - so they had to stuff them into sacks.

Previously, hunters buried tugs in deep holes away from the river. Now, they have found more innovative ways to deal with fish that aren't usually needed.

At an event earlier this year, sacks in Suckermouth were handed over to a local entrepreneur in hopes of trying to turn the fish into a form of charcoal called biochar.

Some local universities have also begun to study the possible use of Suckermouth. One university research article explores the potential of Suckermouth collagen for drug use, while another argues it is used as a fertilizer or even a kind of leather.

In some cases, hunters even ate the fish they caught, although it depends on which river they took from.

While some people think red-tailed or African catfish are considered delicious, Suckermouth, also known as “manifest fish” in India, is an attractive snack option, but it is not without problems with the fast river grill.

Mohd Zulkifli Mokhtar told Al Jazeera that dozens of hunters broke their fast during the St. Muslim month of Ramadan.

"But if it comes from the Langat River, it's OK," Zulkivley said. Dozens of Suckermouth, trapped in the less polluted Langat River, located in the Bangi River about 25 kilometers (16 miles) south of Kuala Lumpur, were ditched, marinated with Satay, marinated with Satay and grilled on a baking tray.

Studies from Bangladesh and Indonesia have found that catfish have high levels of heavy metals and pollutants. A 2024 article by Teknologi University Mara in Malaysia cited a study that showed that Suckermouth's pollutant levels are "significantly affected by pollution levels in the river".

“It would be worse if we don’t act now”

Although Malaysia's Fisheries Ministry said there is no record of local species endangered due to invasiveness, local fish are still at risk.

Local fish either face prey or have to fight for survival, and the department found in a survey that 90% of the fish in the Six Rivers in Selangor and Kuala Lumpur are now foreigners.

Adnan Hussain, director of the department, said various measures have been taken, including releasing about 33.6 million domestic fish and prawns into rivers across the country from 2021 to 2025 to "balance the effects of invasive fish."

Late last year, the Selangor state government also proposed a plan to pay anglers a Malaysian ringgit ($0.23) per kilogram (2.2 pounds) removed from the two rivers. A caught fish will be turned into animal feed and organic fertilizer, an official said.

The import restrictions on certain foreign aquatic species were also imposed last year, including entire species and groups, and fishermen were imposed, adding that plans and cooperation with fish hunters also helped to address the issue.

Adnan said in a river in Selangor that the number of invasive fish caught has dropped from 600 kg (1,300 pounds) after a removal program dropped from 600 kg (1,300 pounds) to just 150 kg (330 pounds) four to five months after an eradication program.

However, Amirrudin Ahmad, a fish researcher at the Mengsheng Department of the University of Malaysia, said it was "almost impossible" to completely eliminate the invasive fish in the country.

"So many species live in (local bodies of water) and are completely unfeasible by poisoning water, thus eliminating invasive species," he said.

He further warned that climate change-induced temperature rises may even allow species such as predatory Mekong red-tailed fish to proliferate in Malaysia’s cool upstream waters.

“They stay here,” Amir Ruddin said.

"It's simple, the environment is mostly similar to their home country, or these species are highly adaptable," he said.

It's an ecological war that can never be truly won, and it's a point that Haziq and his fish hunters are fully aware of. He said that almost every river visited recently has only invasive fish.

But their mission will continue, coupled with hunting and public awareness, has stimulated thousands of people to follow his social media videos, he added.

"Yes, this fish is not going to completely disperse from our river," he told Al Jazeera.

"But if we don't take action now, it will be worse," he said.

He added: “It is better to act than to act alone.”

“At least we can reduce the population instead of letting it take over our local fish altogether.”