Alien Fish Make Up 95% of Ampang Hilir Lake Records as Malaysia Weighs Species Bans

A lake dominated by introduced fish

At Kuala Lumpur's Tasik Ampang Hilir, Fisheries Department records cited by Agriculture and Food Security Ministry secretary-general Datuk Seri Isham Ishak counted 146 alien fish and just eight native fish among 154 recorded. That puts the alien share at about 95%, with roughly 18 introduced fish for every native fish recorded.

The figures have prompted calls for stronger controls on aquarium releases, more removal programmes and possible bans on species that threaten Malaysia's freshwater ecosystems. At the lake, which covers 16 hectares, a fishing programme removed more than 1,800 kilograms of invasive fish in four hours.

Isham spoke at the inland fisheries sustainability and alien fish removal programme at Tasik Ampang Hilir on October 17. He called for decisions guided by data, public education and cooperation between government agencies, businesses and nongovernmental organisations.

The department's figures were also described publicly as 146 alien species and eight native species among 154 species. The more detailed account described 154 fish recorded. For readers, the central finding is the overwhelming alien share in the lake records cited by officials.

An alien fish is a species introduced beyond its natural range. An invasive fish is an introduced species that establishes itself, spreads and causes harm. Isham warned that releasing aquarium fish when they become too large or difficult to care for can damage aquatic biodiversity, meaning the variety of life in the water, and threaten native fish.

The response now connects three tasks: removing established invaders, replenishing native populations and stopping new introductions. Research from Klang Valley adds a fourth concern, the condition of the rivers and lakes where released fish may settle.

What the removal programme achieved

Fisheries Department deputy director-general for development Datuk Azahari Othman said 150 anglers caught more than 2,000 invasive fish during the four-hour programme. The catch weighed more than 1.8 tonnes, showing how much introduced fish could be removed during a single organised effort.

About 250 people from seven agencies and organisations participated in the wider programme. Activities used seine nets, cast nets, fishing lines and fish traps. Seine nets gather fish by drawing a net through or around an area of water, while cast nets spread over a smaller patch before being retrieved.

The campaign has operated since 2022. Across 2022 to 2025, the alien fish removal programme recorded a cumulative catch of 19.74 tonnes. The event catch and the campaign total measure different periods: one covers four hours, while the other covers several years of removal work.

Isham said catching alien fish needed to become more intensive. The scale of the cumulative catch explains why officials are also targeting the decisions that put fish into public waters, rather than relying entirely on repeated fishing events.

Native fish releases come with different totals

Agrobank released 1,400 native fish fry into Tasik Ampang Hilir, comprising 1,100 baung and 300 lampam sungai. Fry are young fish released to help replenish a population. Baung accounted for nearly four fifths of the bank's contribution.

Azahari gave a larger release figure for the programme: 32,500 native fry and 11 adult fish. The relationship between that total and Agrobank's 1,400 fry was not specified. Across Malaysia, the Fisheries Department released 58.6 million fish and prawn fry between 2021 and 2025 to replenish populations and restore affected aquatic ecosystems.

Agrobank chief development officer Ahmad Arif Abu Bakar said restoration needed public understanding as well as releases. He described the responsibility of aquarium owners:

"The public needs to understand their responsibility in maintaining the ecosystem, including not releasing pet fish into rivers or lakes when the fish grow larger," he said.

Why aquarium shops matter

A study published in Scientific Reports on October 14, 2020, provides a detailed picture of the fish available to Klang Valley aquarium owners. Researchers surveyed 60 ornamental fish stores during 2019 and documented 251 alien fish species and 42 native species.

The ornamental fish study found that alien species made up 85.66% of the species recorded in the trade. That is almost six alien species for every native species, calculated from the study's totals of 251 and 42.

The researchers described the aquarium trade as Malaysia's second most important route for alien fish introductions into inland waters, after aquaculture, or farming fish and other aquatic animals. They identified several reasons owners might release fish: excessive size, aggression, rapid breeding or a loss of interest in keeping them.

Goldfish appeared in 83.3% of the surveyed stores. Of the alien species documented, 44% originated from South America, 25% from Asia and 20% from Africa. A fish can be native to another part of Asia and still be alien to Malaysian waters because natural ranges follow habitats and geography, rather than continental labels.

The shop findings help explain why Isham's message extends beyond people visiting the lake. Owners make the final decision to release a fish, but retailers influence which species enter homes and what buyers understand about caring for them as they grow.

Which fish pose the greatest risk?

Isham said plecos, commonly called ikan bandaraya, accounted for 83% of recorded invasive fish landings nationwide. Peacock bass, also known as ikan raja, accounted for another 13.8%. Together, the two groups represented 96.8% of those recorded landings.

Landings are fish brought in after capture. The figures identify the fish dominating removal catches across the country, giving authorities a practical focus for fishing campaigns and public warnings.

The aquarium trade study also assessed invasion risk for 23 selected species. Using the Fish Invasiveness Screening Kit, known as FISK, researchers classified nine, or 39.1%, as posing a high risk. The tool uses questions about a fish's biology, ecological needs and history of becoming established outside its natural range.

The researchers calibrated a score of 17 as the dividing point for high invasion risk in their assessment. A second method, the Fish Invasiveness Screening Test, placed seven species in its high risk group: north African catfish, goldfish, common carp, guppy, flowerhorn, redtail catfish and suckermouth catfish.

The two methods produced different totals because they assess risk differently. Both give authorities a way to examine individual species before deciding which fish need tighter controls.

River research connects invasions with habitat conditions

A 2021 study published in Animals examined six Klang Valley rivers: Pusu, Langat, Gombak, Klang, Tekala and Semenyih. Researchers sampled fish and water between January and March 2020, covering stretches averaging about 500 metres in each river.

The river invasion study recorded 20 fish species, including six alien species. Tilapia accounted for 45.9% of all sampled fish. Alien fish occurrence reached 57% in the Pusu River, 50% in the Langat River and 40% in the Gombak River. Its fieldwork covered rivers, with Tasik Ampang Hilir outside the study area.

The researchers found that alien fish occurrence was associated with poorer water quality, including higher ammonia nitrogen and nitrite and lower dissolved oxygen. Fish depend on oxygen dissolved in water to breathe. Pollution can change which species are best able to survive in a habitat.

Alien tilapia and sailfin catfish were also associated with more polluted surroundings and easier human access to the water. The researchers concluded that human activity and flexible feeding habits could help alien fish establish themselves and become dominant.

Using the Aquatic Species Invasiveness Screening Kit, or AS-ISK, the study assessed five alien species. Four fell into the high invasion risk category, while Barbonymus gonionotus fell into the medium category.

How native fish face pressure

The river researchers examined stomach contents and chemical signatures in fish tissue to understand feeding patterns. Stomach contents show recently eaten food. Chemical signatures can help trace the sources of food used over a longer period.

The findings showed overlap between the diets of alien and native fish, alongside dominance by alien fish in parts of the sampled river community. When species depend on similar food, native fish may face stronger competition for the resources they need to grow and reproduce.

The study described other ways introduced fish can harm native populations, including predation, competition for space, habitat changes and the introduction of diseases. Which pressures matter most depends on the species and the waterway involved.

For restoration at Ampang Hilir, the combined findings point to a practical challenge: newly released native fish need suitable living conditions while established alien fish are being removed. Catching invaders, improving habitat conditions and preventing further releases address different parts of that challenge.

Malaysia considers restrictions on sales

Isham said the ministry was reviewing ways to tighten existing regulations, including possible bans on species identified as threats to local ecosystems. He also directed a warning at businesses selling ornamental fish:

"We also urge ornamental fish dealers to refrain from selling invasive fish to the public. We may impose a total ban on certain species that pose a threat to our waters," he said.

The ministry had not announced a final list of species, a decision date or an implementation timetable. The immediate appeal was for dealers to avoid selling invasive fish and for owners to stop putting unwanted pets into lakes, rivers, dams and public waterways.

Isham linked that request to the risk of a damaging habit becoming accepted behaviour. Explaining why public education formed part of the response, he said:

"If we do not educate, this matter will become a culture that is difficult to curb and will become a long-term problem," he said.

The aquarium research gives that appeal a concrete basis. A trade containing hundreds of alien species creates many opportunities for introductions, while species screening can help direct restrictions toward fish judged most likely to establish themselves and cause damage.

A national campaign with a longer history

Isham said 37 invasive fish removal programmes had been held during the year of the announcement, with the total expected to exceed 40 by year end. The effort extends beyond the capital: Perak accounted for 50.3% of recorded foreign fish intrusion cases, followed by Negri Sembilan at 16.5% and Selangor at 13.3%.

Together, those three states accounted for 80.1% of the recorded cases. Perak's share alone was greater than the combined 29.8% recorded in Negri Sembilan and Selangor, showing the concentration of cases in the department's figures.

The research and removal programmes developed across several years:

• 2019: Researchers surveyed 60 ornamental fish stores in Klang Valley.
• January to March 2020: Researchers sampled fish and water in six Klang Valley rivers.
• October 14, 2020: Scientific Reports published the aquarium trade study.
• 2021: Animals published the river study linking alien fish occurrence with habitat and water conditions.
• 2021 to 2025: The Fisheries Department released 58.6 million fish and prawn fry nationwide.
• 2022 to 2025: The alien fish removal programme recorded a cumulative catch of 19.74 tonnes.

Ampang Hilir brings those strands together in one public lake. Officials are removing invasive fish and adding native fish, while research points toward action at shops, in homes and around the waterways where introductions occur.

Key Points

• Fisheries Department records cited for Tasik Ampang Hilir put the alien fish share at about 95%.
• A four-hour programme removed more than 1,800 kilograms of invasive fish, with over 2,000 fish caught by 150 anglers.
• Agrobank released 1,400 native fry; a larger programme figure given by the Fisheries Department was 32,500 fry and 11 adult fish.
• Plecos and peacock bass together accounted for 96.8% of recorded invasive fish landings nationwide.
• A survey of 60 Klang Valley aquarium stores documented 251 alien fish species and 42 native species.
• The ministry is considering tighter controls and possible species bans while urging owners to stop releasing aquarium fish into public waters.