Taxonomy & naming
Rasbora kottelati was described by Lim in 1995. The Catalog of Fishes (Eschmeyer, CAS) records the valid combination as Rasbora kottelati Lim, 1995; it remains in the large, paraphyletic genus Rasbora — a holding genus that still contains a broad sweep of Southeast Asian cyprinids that have not yet been reassigned to the smaller genera (Boraras, Trigonostigma, Brevibora, Trigonopoma, Kottelatia and others) carved out of it in the late twentieth and early twenty-first centuries.
The species is named after Maurice Kottelat, the Swiss ichthyologist whose decades of work on Southeast Asian freshwater fishes have produced an enormous body of revisionary taxonomy for this region. The species belongs to the family Danionidae, the expanded danio family that encompasses rasboras, danios and their relatives following the dissolution of the traditional Cyprinidae into smaller families.
Morphology
Rasbora kottelati is a slender, laterally compressed cyprinid reaching a maximum recorded length of 3 in standard length (SL). Like many members of the genus it has a streamlined, fusiform body suited to open water in sluggish lowland streams. The lateral line is well developed and the mouth is terminal, positioned for mid-water feeding.
Detailed colour description data for this species is sparse in the available literature. As a peat-swamp rasbora it likely displays the semi-transparent, laterally marked flanks typical of many Bornean Rasbora species from similar blackwater habitats, often with a dark lateral stripe or iridescent sheen visible in life.
Habitat
This species is endemic to the lowland peat-swamp forests of northwestern Borneo, with records confined to Sarawak (Malaysian Borneo) and Brunei Darussalam. Its type locality encompasses the slow, dark streams and swamps that drain through peat forest — among the most chemically distinctive freshwater habitats on Earth. The water is tannin-stained to a deep amber or brown, extremely soft, and intensely acidic, with pH values recorded at 4.1–6.1 on FishBase.
Peat-swamp water is not merely acidic: it is mineral-poor, low in dissolved oxygen in stagnant areas, and laden with humic acids leached from partially decomposed plant matter. Temperatures in these equatorial lowlands are stable and warm year-round. Rasbora kottelati is therefore a specialist of a very particular physical-chemical niche, not a generalist tolerant of fluctuating conditions. iNaturalist specimen records confirm the species has not been observed outside this northwestern Bornean range.
Feeding
Rasbora kottelati is presumed to be an omnivorous micropredator in the manner of the wider genus, taking small invertebrates — aquatic insects and their larvae, small crustaceans — from the water column and surface film, supplemented by organic detritus and microorganisms abundant in the nutrient-rich peat-swamp environment.
In the aquarium it accepts live and frozen foods readily. SeriouslyFish records it taking bloodworm (chironomid larvae), Daphnia and brine shrimp (Artemia), alongside good-quality flake. Offering a varied diet that includes live or frozen invertebrates helps maintain condition in this blackwater specialist.
Mating
Rasbora kottelati is an egg-scattering, non-guarding spawner. There is no nest construction, no pair bond and no parental investment beyond the act of spawning itself. In courtship a driving male pursues a gravid female through vegetation or over submerged leaf litter, and eggs and milt are released together in brief bursts.
Spawning may be triggered by seasonal rainfall patterns in the wild, which alter water depth, temperature and chemistry in the peat-swamp environment. Soft, acidic conditions that closely mimic the blackwater type locality are likely to be the most reliable spawning stimulus in captivity.
Breeding
Specific breeding accounts for Rasbora kottelati in the aquarium literature are sparse. By analogy with other peat-swamp rasboras, it is likely to scatter adhesive or weakly adhesive eggs over fine-leaved plants, moss, roots or submerged leaf litter, with no parental care thereafter. Adults should be removed after spawning to prevent egg predation.
Replicating the native water chemistry — very soft, acidic water at pH 5.0–6.5 and temperature 75–81 °F — is expected to be important for egg viability and larval development, as is typical for blackwater specialists from the peat forests of Sundaland.
In the aquarium
Rasbora kottelati is a peaceful, shoaling species that SeriouslyFish recommends keeping in groups of at least eight to ten individuals. Its calm temperament makes it compatible with other small, non-aggressive fishes adapted to soft, acidic water — dwarf gouramis, small loaches and similarly sized blackwater rasboras or danionids are suitable companions.
The aquarium should be set up to replicate the peat-swamp environment: very soft, acidic water (pH 5.0–7.0, hardness 2–10°H) at 73–82 °F, low to moderate lighting, tannin from dried leaves or driftwood, and dark substrate. Good filtration with gentle flow is important, but the species is not adapted to fast current. It is a capable jumper, so a tight-fitting lid is essential. Its blackwater requirements make it less suitable for the typical hard-water community tank.
Conservation
The IUCN Red List assessed Rasbora kottelati as Least Concern (LC) in a 2019 assessment. While this status indicates no immediate risk of extinction at the time of assessment, it must be read in the context of the species' narrow endemic range in northwestern Borneo and its strict dependence on peat-swamp forest — one of the most threatened ecosystems in Southeast Asia.
Peat-swamp forests in Sarawak and Brunei have been extensively drained for agricultural conversion, particularly oil palm, and degraded by logging, fire and water extraction. These pressures directly degrade the blackwater chemistry and hydrological connectivity that obligate peat-swamp species require. The species' restriction to a small geographic footprint and a highly specialised habitat means that habitat loss, even within its current range, could shift its conservation status rapidly if the peat forest continues to contract.