Janitor Fish Devouring Jakarta's Rivers, Turns Out It Wears 'Armour'
In recent times, the presence of janitor fish in various Indonesian waters has come under scrutiny. In Jakarta, the Provincial Government has conducted mass capture operations for janitor fish in several waterways.
Regarding the janitor fish, Triyanto, a researcher from the Centre for Limnology and Water Resources Research (PRLSDA) under the National Research and Innovation Agency (BRIN), revealed that the fish’s high resilience makes its population difficult to control and potentially causes ecological, economic, and social impacts.
Triyanto explained that the janitor fish is classified as an invasive alien species because it does not originate from Indonesian waters. This fish has a very rapid reproductive capacity with a large number of eggs or high fecundity. Additionally, its life cycle is relatively short until reaching adulthood, and it can reproduce throughout the year.
According to him, another factor strengthening the dominance of the janitor fish is its very broad adaptive ability. This species can survive in low-quality environmental conditions, such as waters with low oxygen levels or high organic pollution.
“Its spread is rapid and effective, and it has negative impacts—ecological, economic, and social,” said Triyanto to CNBC Indonesia on Thursday (23/4/2026).
He also highlighted the physical characteristics of the janitor fish, which is often said to have “armour.” This term refers to the protective body structure in the form of dermal bone plates (bony plates) under the skin.
Triyanto emphasised that when the population of an invasive species like the janitor fish has dominated an ecosystem, control becomes very difficult. Scientific studies show that control efforts must be carried out holistically.
“Because efforts need to be made holistically from the root cause, to control the janitor fish population,” he explained.
Environmental improvements are necessary so that other fish species, including natural predators, can return in balanced numbers.