Taxonomy & naming
Betta unimaculata was originally described by Popta in 1905, making it one of the earlier-known members of what is now called the unimaculata species group — a clade of large, paternal mouthbrooding bettas distributed across Borneo and the southern Philippines. Eschmeyer's Catalog of Fishes treats the valid name as Betta unimaculata (Popta, 1905); the parenthetical authority indicates the species was originally placed in a genus other than Betta before being transferred.
The unimaculata group is distinguished from bubble-nesting Betta by its reproductive mode — paternal oral incubation — and by its generally larger body size. Other members of the group include Betta macrostoma, Betta ocellata, and Betta gladiator. Molecular and morphological studies of the genus Betta have progressively refined the groupings within this diverse lineage, and the unimaculata group is now well-supported as a natural assemblage. The specific epithet unimaculata is Latin for 'one-spotted', referring to a characteristic spot on the body.
Morphology
Betta unimaculata is a large betta, reaching up to 5 in total length — substantially bigger than the familiar fighting fish and most of its bubble-nesting relatives. The body is elongate and moderately compressed, with a large mouth suited to oral incubation of eggs and fry. Like all bettas, it possesses the suprabranchial labyrinth organ that allows it to breathe atmospheric air directly, supplementing gill respiration.
Coloration in the unimaculata group tends toward brown, olive, and iridescent blue-green tones rather than the intense reds and blues of domesticated Betta splendens. Males develop broader heads, more extended unpaired fins, and more vivid iridescent scaling than females, particularly when displaying. The characteristic spot referenced in the name is visible on the caudal peduncle or tail region. Females are generally smaller and plainer, with more rounded fins.
Habitat
Betta unimaculata is endemic to the upper Kayan (Kajan) and Howong river drainages of east Borneo, in the Indonesian province of Kalimantan. It occupies clear, flowing headwater streams and isolated elevated pools — habitats quite different from the stagnant rice paddies and peat swamps associated with many other Betta species. The presence of marginal vegetation, leaf litter, and submerged roots characterises its microhabitat, providing cover and foraging substrate.
Water conditions in these highland Bornean streams are cool to warm and tend toward the acidic: the Seriously Fish profile records pH around 5, consistent with the soft, slightly acidic character of upland Bornean drainages. FishBase gives a wider reported range of pH 6.5–7.5 with temperatures of 70–77 °F, reflecting variation across collection localities and seasons. As a labyrinth fish, Betta unimaculata can tolerate reduced dissolved oxygen by surfacing to breathe air, but the flowing, clear streams it inhabits are generally well-oxygenated relative to peat swamp habitats.
Feeding
Betta unimaculata is a carnivore that feeds primarily on insects, small invertebrates, and zooplankton in the wild. Its large size and powerful jaws compared with smaller bettas give it the ability to take sizeable prey items. Hunting likely occurs at the water surface and through the water column among leaf litter and root tangles.
In captivity the species accepts a variety of live and frozen foods, including Daphnia, Artemia (brine shrimp), and bloodworm. Live foods are particularly valuable for conditioning breeding pairs and encouraging spawning behaviour. A diet weighted toward meaty prey items better reflects natural feeding ecology than plant-based or flake-heavy diets.
Mating
Betta unimaculata is a paternal mouthbrooder: spawning involves a typical anabantoid embrace in which the male wraps around the female to fertilise eggs, but instead of building a bubble nest, the male gathers the fertilised eggs into his mouth for incubation. The eggs and milt are released in small batches across multiple embraces during a spawning bout.
Males of the unimaculata group display with extended fins and heightened iridescence to court receptive females. Competition between males can be intense, and the species is best managed as isolated pairs or in large, well-structured aquaria where subordinate animals can retreat. The male's large mouth — an adaptation to mouthbrooding — is a distinguishing feature that becomes apparent when watching courtship.
Breeding
Following spawning, the male holds the fertilised eggs in his buccal cavity for roughly 10 to 14 days, during which time he does not eat. This is a demanding fast for a fish of this size; males should be in excellent condition before breeding is attempted. The female should ideally be removed from the breeding tank once the male has taken up the eggs, to reduce stress.
At the end of the incubation period, the male releases free-swimming fry that are already relatively large and well-developed compared with the fry of bubble-nesters. First foods for the fry can include small live items such as Artemia nauplii or microworm. The male may continue to gather the fry back into his mouth if they are disturbed in the first days post-release. Raising Betta unimaculata to adulthood requires clean, stable water and appropriately sized prey throughout the growth period.
In the aquarium
Betta unimaculata is not suited to a standard community aquarium. Its size, its need for live or frozen meaty foods, and its territorial disposition toward conspecifics — particularly between males — make it a specialist species best kept as a dedicated pair or in a large, heavily furnished tank. It is peaceful toward dissimilar, non-aggressive tankmates of appropriate size, but males will fight.
The aquarium should replicate the cool, clear, lightly acidic conditions of the highland Bornean streams the species inhabits: temperatures in the low-to-mid 20s Celsius, soft to moderately soft water, and pH on the acidic side of neutral. Leaf litter, driftwood, and dense planting provide cover and help maintain the slightly tannin-stained conditions the species finds natural. Filtration should maintain water quality without creating strong currents — gentle flow is appropriate. As a labyrinth fish, the species must have unobstructed access to the water surface to breathe air; keeping the water level a few centimetres below the tank rim and maintaining a warm, humid air gap above the surface is good practice.
Betta unimaculata appears in the Indonesian ornamental fish trade and is kept by a dedicated community of wild-betta specialists. Most hobbyist stock is captive-bred. Its size and mouthbrooding behaviour make it one of the more rewarding of the large Betta to keep for those with the appropriate setup.
Conservation
Betta unimaculata is assessed as Data Deficient (DD) by the IUCN Red List (2025 assessment). The Data Deficient rating reflects a lack of sufficient information to determine population size and trends rather than a lack of concern; endemic species with restricted ranges and exposure to habitat pressure and trade are often flagged as conservation priorities even in the absence of formal declining-population data.
The species is endemic to east Kalimantan, Indonesia, and has been documented in the Indonesian online wildlife trade — appearing on platforms such as Shopee, Tokopedia, and Lazada. Research by Arifah et al. (2025) found that approximately 26 percent of wild Betta species traded online in Indonesia lack sufficient conservation evaluation, placing them in the Data Deficient or unevaluated categories. Ongoing habitat conversion in Kalimantan — including forest clearance for palm oil and logging — threatens the integrity of the highland stream habitats this species depends on. Sourcing captive-bred stock is the most straightforward step an aquarist can take to reduce pressure on wild populations.