New Species Fish in Mahakam River Reflects Ecosystem Condition

Indonesian researchers have identified and formally described a previously undocumented species of freshwater fish found only in the Mahakam River basin in East Kalimantan, marking a significant addition to the catalog of the country’s endemic biodiversity.

The new species, named Desmopuntius mahakamensis, is a small cyprinid — a family of fish that includes carps, barbs, and minnows — distinguished by several unique physical and genetic features. The findings were published in the peer-reviewed journal ZooKeys in late October 2025.

“This new species is currently known only from the Mahakam River drainage in East Kalimantan,” said Tonisman Harefa, lead author of the study from Indonesian Agency for Research and Innovation (BRIN). “Most of the specimens were collected from small tributaries and nearby lakes, and the discovery underscores both the remarkable diversity and the vulnerability of freshwater ecosystems in the region.”

The Mahakam River — one of Borneo’s longest waterways — supports complex freshwater habitats that are home to commercially and culturally important species as well as unique endemic organisms. Desmopuntius mahakamensis is among the latest to be formally identified from this system, joining other distinctive riverine fauna that have been the subject of scientific and conservation attention.

Taxonomic Confirmation

The newly identified species reaches less than nine centimeters in length, with a slender body less than two centimeters wide. It sports five to six horizontal black stripes along its body against a silvery-gray background, an arrangement that initially led field biologists to tentatively label it as a striped Puntius species until formal analyses were completed.

According to the ZooKeys publication, the species is distinguished from related Desmopuntius congeners by a combination of anatomical traits, including the number of lateral line scales, gill raker counts, fin ray counts, and specific coloration patterns not seen in its closest relatives. Genetic comparisons supplemented these findings, revealing significant divergence from other known species.

Co-author Haryono, also of BRIN, said in an interview that the research team used integrative taxonomic methods — combining detailed morphology with molecular analysis — to confirm the species’ distinct status. “Without DNA data and careful morphometric work, we could have easily overlooked this fish as a variant of a known species,” he told AP.

The description of D. mahakamensis brings the total number of recognized species in the genus Desmopuntius to nine. The genus includes populations found in several other major Indonesian rivers, but until now, none had been documented from the Mahakam system.

Conservation Concerns

Environmental experts say the discovery highlights both the richness and the escalating threats that face freshwater environments in Kalimantan. The Mahakam River — which flows nearly 938 kilometers from its headwaters near the Indonesian-Malaysian border to the Makassar Strait — is vital to local communities for water, food, and transport. But the ecosystem is under mounting pressure from deforestation, mining, pollution, and infrastructure development.

The river is also home to the critically endangered Mahakam dolphin (Orcaella brevirostris), with government estimates indicating its population has dwindled to fewer than 70 individuals. Conservationists say the plight of the dolphin is a stark indicator of broader ecological stress in the basin.

“This discovery comes at a time when the Mahakam’s freshwater biodiversity is threatened by human activities,” Harefa said. “It is a reminder that even small fish species — which may not receive the same attention as larger mammals — are vital components of the ecosystem and deserving of protection.”

Local scientists and environmental groups have called for increased conservation measures for the Mahakam River, including stricter regulation of mining effluents, sustainable land-use planning, and enhanced monitoring of aquatic biodiversity. Such efforts, they argue, would help safeguard not only newly discovered species like D. mahakamensis but also the broader web of life that depends on the river’s health.

Researchers noted that much of Indonesia’s freshwater biodiversity remains poorly documented. Many river systems, particularly in Borneo and Sumatra, harbor species that are unknown to science but may be at risk from rapid environmental change.

“Discoveries like this are not just exciting for science,” said Tedjo Sukmono, a co-author of the research. “They are critical evidence that underscores the need for habitat protection. What we don’t know, we can easily lose.”

The researchers said further expeditions and studies are planned for other understudied parts of the Mahakam basin. They hope ongoing work will continue to illuminate the river’s biodiversity and inform conservation strategies aimed at preserving this unique freshwater ecosystem. (Sulung Prasetyo)

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