Taxonomy & naming
Betta mandor was formally described by Heok Hee Tan and Peter K.L. Ng in 2006. It is placed in the foerschi group, one of the species-group assemblages within the large and taxonomically complex genus Betta (family Osphronemidae). The foerschi group unites a set of small, paternal mouthbrooders from Borneo and adjacent islands that share broadly similar ecology and reproductive biology. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the authority for the valid name Betta mandor Tan & Ng, 2006.
The specific epithet mandor is a toponym, derived from the town and district of Mandor in Kabupaten Landak, West Kalimantan, Indonesia, which lies within the lower Kapuas drainage and serves as the type locality. The use of a toponym rather than an eponym places the species firmly in its biogeographic context — Mandor is a name familiar to naturalists as the site of a historical nature reserve in West Kalimantan.
Morphology
Betta mandor is a small fish, with published size records ranging from around 2–2.5 in standard length (SL) to approximately 3 in total length (TL) in the largest individuals. It shares the compact, somewhat laterally compressed body plan typical of the foerschi group: an arched dorsal profile, large eyes relative to head size, and relatively rounded fins compared to the elongated finnage seen in domesticated fighting fish.
Sexual dimorphism is moderate. Males are reported to show more intense colouration, including red opercular bars, and tend toward deeper body colour overall. Females display gold or yellow opercular bars in place of the male's red. The colouration pattern of the opercular region is one of the key recognition features in this species group and plays a direct role in mate recognition and spawning behaviour. Juveniles and non-displaying individuals are considerably plainer, making identification in the field more difficult.
Habitat
In nature Betta mandor inhabits forest swamp streams and pools within the lower Kapuas basin of West Kalimantan, Indonesian Borneo. The waters it occupies are blackwater: heavily stained with dissolved humic and fulvic acids derived from decomposing organic matter in surrounding peat-swamp forest, producing the characteristic tea-coloured water of these systems. This humic staining is associated with extremely soft, very acidic conditions — the species has been recorded at pH values around 4.0, with negligible general and carbonate hardness.
As a labyrinth fish, Betta mandor possesses a suprabranchial labyrinth organ that supplements gill respiration, allowing it to extract oxygen directly from air breathed at the water surface. This adaptation is a direct response to the low dissolved-oxygen levels that characterise the warm, stagnant or very slow-flowing pools of intact peat-swamp forest. The fish is heavily shaded habitat: forest canopy over its streams severely limits light penetration, and the humic water itself is opaque at depth. Like other foerschi-group bettas it is understood to be solitary in habit, with adults holding small territories in the dense cover of leaf litter, submerged roots, and marginal vegetation.
Feeding
Betta mandor is a carnivore in the wild, feeding primarily on small insects and aquatic invertebrates that fall or drift into the slow-moving forest pools and streams it inhabits. Insects — both adult terrestrial forms landing on the water surface and larval aquatic stages — form the bulk of the diet, supplemented by other small invertebrates such as worms, crustaceans, and similar prey appropriate to a small predator of its size.
In the aquarium the species accepts live and frozen invertebrate foods readily, and most individuals can be trained onto high-quality prepared foods over time. Small live or frozen Daphnia, bloodworm, micro-worms, and similar items are appropriate staples. The small mouth size typical of the foerschi group constrains prey dimensions and means appropriately small food items should be offered, particularly when conditioning fish for breeding.
Mating
Betta mandor is a paternal mouthbrooder. Spawning is initiated by the female, who approaches and courts the male, a behaviour pattern noted for several mouthbrooding bettas in which the typical anabantoid sex-role is partly reversed. The pair engages in the characteristic nuptial embrace of bettas, with the male wrapping around the female as eggs and sperm are released simultaneously.
Following the embrace, the fertilised eggs are collected — typically by the male — and taken into the buccal cavity. The male then retires to sheltered cover to incubate the clutch. During this period he does not feed, devoting the entire incubation phase to brooding. Males in the foerschi group display subdued or cryptic behaviour while mouthbrooding, avoiding conspicuous movement that might attract predators. The opercular colouration differences between the sexes, especially the distinctive bar patterns, are likely important visual signals during the courtship sequence.
Breeding
Incubation of the eggs inside the male's mouth lasts approximately 12 to 17 days, with around 15 days being typical under normal temperatures; warmer water shortens the incubation period slightly. During this entire interval the male abstains from feeding. The fry are released as free-swimming juveniles capable of taking appropriately sized first foods immediately upon release, which is characteristic of mouthbrooding bettas — the extended parental care substitutes for the early fragility typical of egg-scatterers.
In the aquarium, breeding is most reliably achieved by maintaining a pair or small group in a dedicated tank with soft, very acidic water (pH around 4.0–4.5), minimal hardness, and warm temperatures around 77–82 °F. Dense cover with leaf litter, driftwood, and floating plants provides the security the male needs to brood undisturbed. The male should not be disturbed once brooding begins, as stress may cause him to swallow or prematurely release the clutch. Experienced keepers recommend removing the female after spawning if the pair is kept in a small tank, to prevent the male from being harassed during his brooding fast.
In the aquarium
Betta mandor is an uncommon species in the hobby, appearing occasionally through specialist breeders and wild-betta interest groups rather than in mainstream trade. It is a blackwater specialist that demands soft, very acidic water: pH around 4.0 is optimal, with minimal hardness and temperatures in the range of 72–82 °F. Replicating these conditions requires the use of reverse-osmosis water or similarly soft source water, buffered down with peat, blackwater extract, or Indian almond leaves. Standard tap water — even dechlorinated — is unsuitable for a fish whose native water is essentially dilute organic acid.
The tank should be densely furnished with leaf litter, driftwood, and floating plants to create the shaded, well-structured environment the species requires for security and natural behaviour. As a labyrinth fish it must have access to warm, humid air at the water surface — a tight-fitting cover that traps warmth above the waterline is important, especially in cooler rooms. Filtration should produce very gentle flow; the species is not adapted to currents. B. mandor is a peaceful fish unsuited to a busy community; it does best in a species tank or with other soft-water, non-aggressive micro-fish. Given its Endangered status, acquisition of captive-bred stock from responsible specialist breeders is strongly preferred over wild-caught individuals.
Conservation
Betta mandor is assessed as Endangered (EN) on the IUCN Red List. The primary drivers of its threatened status are habitat loss and degradation: the lowland peat-swamp forest of West Kalimantan, where this species is endemic, has experienced severe deforestation for oil palm plantations, pulp wood, and agricultural expansion. Drainage and burning of peat swamps destroys the intact forest hydrology on which blackwater specialists like B. mandor depend — the chemistry of the water, which is generated by slow decomposition of undisturbed peat, collapses rapidly once canopy cover is removed and waterways are altered.
Academic reviews of Betta conservation in Indonesia have also noted pressure from wild collection for the ornamental fish trade, which adds a direct removal pressure to a population already constrained by a naturally restricted range. The type locality near Mandor, West Kalimantan, is within a historically protected reserve, but broader land-use change in the lower Kapuas basin continues to threaten the swamp habitat the species requires. For aquarists, sourcing only captive-bred stock and supporting habitat conservation efforts in Indonesian Borneo represent the most meaningful contribution they can make.