Volunteers, residents and city workers in Jakarta cheered as bulging nets of invasive “janitor fish” were hauled from a reservoir during a mass removal operation aimed at cracking down on the fish in the Indonesian capital.
Authorities said they want to remove at least 10 tons (9 metric tons) of the invasive fish from Jakarta’s waterways, and officials also linked the effort to water-quality concerns along the Ciliwung River.
“Janitor fish” are the local name for suckermouth catfish in the Pterygoplichthys genus. The fish are not native to Indonesia, having been imported decades ago for aquariums because of their ability to consume algae before being released and spreading into Jakarta’s rivers.
AP reported that the fish can grow up to 50 centimeters (nearly 20 inches) and can live 10 to 15 years. It also said experts have long warned that unchecked invasive species can destabilize freshwater ecosystems, especially in densely populated urban areas like Jakarta.
Dian Rosleine, an ecologist from Bandung Institute of Technology, said the fish’s adaptability is very high, enabling them to survive even in polluted conditions. She described janitor fish as “biological indicators that the water is in poor condition,” and said the Ciliwung’s current state—carrying untreated household waste and industrial runoff through dense neighborhoods—creates conditions that favor the fish.
According to the report, the cleanup campaign began last week and was carried out simultaneously across all five administrative cities of Jakarta. AP said the operation involved hundreds of personnel, including firefighters, disaster officers and local residents, and it reported that officials have netted and buried more than seven tons of the fish across the city within a week.
On Friday, the operation included cleanup at a 6-meter-deep (19-foot-deep) reservoir in East Jakarta’s Ciracas neighborhood, where city workers collected about 320 kilograms (705 pounds) of janitor fish, according to AP. Workers hauled the fish into red barrels along the reservoir before burying them.
East Jakarta Mayor Munjirin told reporters during the cleanup that janitor fish populations have reproduced at a notable level and have also fed on native species. He said their impact extends beyond ecosystem destruction, contributing to structural damage to riverbank and embankment walls, and he said the coordinated operation would mark the start of a sustained effort that includes regular monitoring and removal.
Munjirin also said the program’s method would be reviewed after Indonesia’s Ulema Council, or MUI, raised concerns about perceived cruelty, pledging that all fish will be dead before burial. AP reported that MUI’s fatwa commission warned that burying janitor fish alive amounts to a violation of animal rights enshrined in Islamic teaching.
Jakarta Governor Pramono Anung said the cleanup method will require the fish to be dead before burial at designated sites, with hygiene standards applied to block their return to rivers or trade. He also suggested Brazil’s model for greater economic benefits, in which fish are turned into charcoal, according to the report.
Still, experts warned that removal is only a beginning. Rosleine said the Ciliwung River requires rehabilitation and that addressing only symptoms without tackling root causes would not provide a lasting solution.