It's Not the Invasion That Needs Fixing, But the Cause!

On 17 April 2026, joint task force officers in Jakarta captured 68,800 suckermouth catfish, weighing nearly seven tonnes, in a single operation. The fish were then buried alive. By 10 April, the total catch had exceeded 12 tonnes. While many in the community responded with admiration, a fundamental assumption needs correcting: a river full of fish is not necessarily a healthy river. Quite the opposite. The abundance of suckermouth catfish in the Ciliwung River is a sign that the ecosystem is in poor condition.

Why has this fish come to dominate the Ciliwung? The suckermouth catfish (Hypostomus plecostomus) is not native to Indonesia. Originating from the Amazon River, it entered Indonesia through the ornamental fish trade. Its success in the Ciliwung is no accident. Its body is covered in scutes, hard bony plates that make it difficult for local predators to consume. It also possesses an auxiliary breathing system that allows it to extract oxygen from the air, enabling it to survive out of water for up to 30 hours and endure water with extremely low oxygen levels. This is precisely the problem: the Ciliwung’s polluted state benefits this fish. Data from the Ministry of Environment and Forestry’s ONLIMO system recorded that 95.5 per cent of the Ciliwung’s water quality was polluted in the first semester of 2025. In such conditions, more sensitive native fish cannot survive. Without competitors and effective natural predators, the suckermouth catfish population has surged dramatically, from 12 individuals in 2011 to 287 in a 2023–2024 study, a 24-fold increase in 14 years.

Before blaming the fish, it is worth examining the root of the problem: why has the Ciliwung River deteriorated to this extent? The suckermouth catfish is a bioindicator, meaning its presence in large numbers reflects a degraded environment. It did not arrive to ruin the river; it flourished because the river was already damaged by domestic and industrial waste continuously flowing into the Ciliwung. This is crucial because it has direct implications for the effectiveness of the response. Catching tonnes of suckermouth catfish without improving water quality is a solution that will never be complete. A single female can produce thousands of eggs per cycle. As long as the river remains polluted, new populations will continue to grow and replace those removed. It is akin to mopping the floor while the roof is still leaking.

Why not simply eat or sell the fish? The answer lies within the fish itself. As a detritus feeder on the riverbed, the suckermouth catfish absorbs and accumulates heavy metals from the sediment through a process called bioaccumulation. Research has found lead (Pb) levels in its flesh reaching 2.2 mg/kg, more than ten times the safe limit of 0.20 mg/kg set by the Indonesian Food and Drug Authority (BPOM). Laboratory tests by the DKI Jakarta Food Security, Marine and Agriculture Office also discovered Salmonella and E. coli bacteria in these fish. Consuming suckermouth catfish from a polluted environment can increase the risk of serious long-term health issues, particularly heavy metal poisoning, whose effects are cumulative and not immediately felt. Ironically, some residents have long used the fish as a cheap processed food ingredient for items like siomay, pentol, and duck feed. This is not due to a lack of care, but because education about the dangers has not reached them. This is a gap that needs filling, not just criticism.

So, what is the solution? The DKI Jakarta government’s burial method has a logical basis: the fish can survive for a long time on land, so their death must be ensured. The incinerator option was rejected due to potential air pollution. However, burial is not without risk. As the fish decompose in the soil, the heavy metals they contain could leach into the ground and contaminate groundwater if the burial site is not chosen with adequate study. Information on this has not yet been openly communicated to the public. There are several more productive alternatives that should be developed. The fish can be used as biomass fuel, burned in high-temperature industrial furnaces with emission filtration systems, trapping heavy metals in the ash while utilising the energy. In the creative industry, the fish’s hard, uniquely textured skin has the potential to be tanned into material for accessories. Several SME communities have begun exploring this, though not yet on a large scale. The idea of turning the fish into fertiliser for crops needs clarification. Processing the fish into fertiliser for food crops risks transferring heavy metals into the human food chain through vegetables or rice. If fertiliser use is pursued, it should only be for non-food plants such as urban trees or ornamental plants. Fundamentally, all these solutions will be meaningless as long as the water quality of the Ciliwung River is not restored. In the upstream areas where water quality is better, the baung catfish, a natural predator of juvenile suckermouth catfish, can still be found. A healthy ecosystem always has its own control mechanisms. Our task is to restore those conditions, not merely to keep chasing the symptoms.

The suckermouth catfish is not an enemy that came from outside. It thrives because of the conditions we have created ourselves through the waste we discard and the river we have neglected for years. Mass capture operations may be necessary as a short-term measure. But if that is all that is done, this problem will not be solved. A healthy river does not need to be ‘cleaned’ of fish.