Parosphromenus phoenicurus

Hidden deep within Sumatra’s blackwater peat swamps of the Kampar River system, the beautiful Parosphromenus phoenicurus lives in a rare and fragile world. In captivity, males reach just under 4 cm, and their vibrant deep-red fins make them instantly recognizable among licorice gouramis.

Beyond their striking appearance, these fish could serve as ecological indicators, as their survival depends on the black, acidic, slow-moving waters of peat swamp forests; ecosystems that are now among the most endangered on the planet. In this way, they can be seen as silent ambassadors of peatland health.

Parosphromenus phoenicurus is a highly localized species of licorice gourami, first described by Ingo Schindler & Horst Linke in 2012.. According to scientific literature, the only known wild population is found in a blackwater swamp near Langgam, part of the Kampar River drainage in Riau Province, central Sumatra (Schindler & Linke).

Biology

This species, endemic to central Sumatra, is restricted to acidic, low-conductivity waters with thick layers of leaf litter and minimal flow. It thrives in habitats with a pH around 5, conductivity below 10 µS/cm, and temperatures near 27 °C. Parosphromenus phoenicurus is therefore highly specialized, living in dark, leaf-covered waters that few other species can tolerate.

Like other anabantids, P. phoenicurus possesses a labyrinth organ that allows it to breathe air from the surface, an adaptation to life in oxygen-poor waters. Members of the genus are micropredators, feeding mainly on tiny invertebrates that they ambush among the leaf litter.

Breeding is thought to coincide with the rainy season, when rising water levels expand their habitat and live food becomes more abundant. During this time, males build bubble nests inside small cavities, where they court females through vivid color displays and ritualized movements. Spawning occurs in a close “embrace,” similar to that of Betta species. After mating, the male takes on the responsibility of guarding the eggs and fry for about 10 days until the young are ready to leave the nest.

Conservation status

Parosphromenus phoenicurus is listed as Critically Endangered on the IUCN Red List. Its entire known range is limited to a small blackwater swamp in central Sumatra, an area increasingly threatened by peatland drainage, deforestation, and land conversion for plantations. These pressures are rapidly shrinking and degrading its fragile habitat, putting the species at high risk of extinction. 

A Species Under Threats 

Indonesia’s peat swamp forests are under severe threat due to a combination of land-use changes and ecological disruptions. One of the main drivers is land conversion for palm oil production, which involves draining peat soils, clearing native vegetation, and replacing it with monocultures. This process not only destroys natural habitats but also leads to alterations in local watersheds, disrupting water flow and causing long-term hydrological imbalances.

Drainage canals dry out the peat swamps, making it highly inhospitable for the wildlife that depends on these systems. Monocultures often leave large areas of bare ground, increasing surface runoff and sedimentation in the remaining peat swamps.

Despite the crucial ecological functions these ecosystems provide—including water regulation, carbon storage, and biodiversity support—most peat swamp areas remain unprotected or poorly managed. As a result, there is a marked decline in species richness, habitat integrity, and the overall health of these unique wetlands. Peat swamps are among Indonesia’s least protected and most threatened ecosystems. E.g: Drainage makes peat extremely flammable; the 2015 El Niño fires consumed 2.6 million hectares of drained peatlands, releasing CO₂ emissions that exceeded those of entire economies on certain days. Deteriorated peatlands no longer act as carbon sinks, they can become major carbon emitters. 

Why It Matters

The peat swamp forests of Sumatra are being lost at alarming rates due to conversion for oil palm plantations, logging, drainage for agriculture, and repeated seasonal fires. Therefore, Parosphromenus phoenicurus could be a flagship species for this habitat type. Its small range, ecological sensitivity, and lack of existing conservation programs make it an urgent priority. Protecting P. phoenicurus is a way to safeguard not only an irreplaceable species but also the entire ecosystem it represents. These habitats help regulate water, store carbon, and provide shelter for countless species. Their decline signals important problems, from erosion and climate change to the loss of biodiversity.

Parosphromenus phoenicurus. Photo credit: The Parosphromenus Project / Fischer