Taxonomy & naming
Betta lehi was formally described by Heok Hee Tan and Peter Ng in 2005 as part of a broader revision of Bornean Betta. The type locality is Stuum Muda stream in the Lundu district of Sarawak, Malaysian Borneo. Eschmeyer's Catalog of Fishes records the valid name as Betta lehi Tan & Ng, 2005; because it was described directly in the genus Betta, no parenthetical authority notation is used.
The species is placed in the pugnax group, a well-supported assemblage of medium-to-large paternal mouthbrooders distributed across Sundaland — the Malay Peninsula, Sumatra, Borneo, and associated islands. Other members include Betta pugnax, Betta prima, and Betta stigmosa. The pugnax group shares a suite of characters including relatively robust bodies, a rounded caudal fin, and the male mouthbrooding reproductive strategy that defines the clade.
The specific epithet honours an individual whose identity is documented in the original description; the eponym follows the conventional latinised patronym form standard in Linnaean nomenclature.
Morphology
Betta lehi is a medium-sized wild betta reaching a reported maximum of 2.5 in standard length — a size typical for the pugnax group, which tends to run larger than the diminutive mouthbrooders such as the albimarginata group. The body is moderately robust and somewhat laterally compressed, with a rounded to slightly pointed head profile and a large mouth suited to egg-carrying during incubation.
Coloration in life includes the patterned flanks and iridescent scale margins characteristic of the pugnax group; males typically show more intense patterning and coloration than females, particularly when displaying or holding eggs. Like all Betta, the species possesses a suprabranchial labyrinth organ — an accessory air-breathing structure above the gill chamber — which allows it to extract oxygen directly from atmospheric air and enables survival in the low-oxygen, organically rich water of its native swamps.
Sexual dimorphism is present but not extreme: males are generally larger and more intensely coloured, and the male's larger mouth — necessary to hold a brood of eggs and early fry — can be a useful secondary character.
Habitat
Betta lehi is endemic to a restricted area of northwestern Borneo spanning the Lundu–Bau district of Sarawak (Malaysia) and the adjacent lower Kapuas basin in Kalimantan Barat (Indonesia). Within this range it inhabits two distinct microhabitat types: acidic forest peat swamps, where pH may fall as low as 3.0–4.0 and tannin-stained blackwater prevails; and the type locality — a clearwater forest stream — where the pH was recorded at a considerably less extreme 6.8. Hardness across its range is low, typically 0–90 ppm.
Peat swamp habitat is characterised by very high organic matter, negligible dissolved solids, very low alkalinity, and warm, stable temperatures. The water column is heavily stained with humic and fulvic acids leached from decomposing vegetation, and dissolved oxygen concentrations can be low. Temperature across the species' range is reported at 72–81 °F (72–81 °F). Dense riparian and overhanging vegetation, submerged root masses, and accumulated leaf litter provide shelter and define the micro-territories that adult bettas defend.
As a labyrinth fish, Betta lehi can breathe atmospheric air, which is an adaptation well-suited to the low-oxygen conditions of peat swamps. Surface access is therefore not merely useful but physiologically necessary.
Feeding
In the wild Betta lehi feeds primarily on small invertebrates — insects at or near the water surface, small aquatic crustaceans, worms, and other invertebrate prey — consistent with the diet documented for the pugnax group more broadly. The species is likely an opportunistic predator that exploits whatever small prey items are seasonally and locally available in the leaf litter and root masses of its swamp habitat.
In captivity the diet is readily satisfied with live and frozen invertebrate foods: Daphnia, Artemia (brine shrimp), bloodworm (chironomid larvae), and similar items. Variety is important for condition; a diet too heavily reliant on a single frozen food type can lead to nutritional deficiencies over time. Some individuals will accept good-quality small pellets, but live and frozen foods form the backbone of a healthy captive diet.
Mating
Betta lehi is a paternal mouthbrooder, a reproductive strategy shared by all members of the pugnax group and well documented within the genus. Courtship is protracted relative to the quick, explosive spawning of bubble-nesting bettas: the male displays to the female over an extended period, flaring his gill covers and spreading his fins to show colour and size. Receptive females respond with appeasement postures.
Spawning involves an embrace in which the male wraps his body around the female — the nuptial embrace characteristic of all Betta — and fertilised eggs are released. Immediately after the embrace, the male collects the sinking eggs in his mouth. This collection behaviour may be repeated through multiple spawning bouts until the male is carrying a full brood. The female plays no further role in incubation or fry care.
Breeding
Following egg collection, the male incubates the fertilised eggs entirely within his buccal cavity (mouth). During this period — reported at approximately 7–12 days for Betta lehi — the male does not eat and may retreat to a sheltered location. The eggs develop in the moist, oxygenated environment of the mouth, and the male continues to hold the increasingly active fry for a short period after hatching before releasing them as free-swimming juveniles.
In the aquarium, breeding is achievable with a well-conditioned pair kept in appropriately soft, warm, acidic water. The male should be given access to a cave or sheltered retreat where he can hold undisturbed. Once the fry are released — typically as fully formed miniature fish — they are capable swimmers and can be raised on small live foods such as micro-worms, baby brine shrimp, and infusoria. Separation of the male from the female after spawning, or of the brooding male from aggressive tankmates, reduces stress during the incubation period.
In the aquarium
Betta lehi is an uncommon species in the hobby, occasionally available through specialist wild-betta importers and breeders. Its care requirements reflect its peat-swamp origins: soft, acidic water with pH in the range of 4.0–6.5, very low hardness (approaching 0 dGH in dedicated setups), and temperatures of 75–81 °F (75–81 °F). Tannin-rich water, achieved with dried leaves, peat filtration, or commercially available blackwater extracts, is beneficial both physiologically and for colouring up the fish.
Filtration should produce minimal flow — a gentle sponge filter or similar provides biological filtration without creating the current that would stress a still-water specialist. Dense cover from live or artificial plants, submerged wood, and leaf litter replicates the structure of the swamp habitat and gives this naturally territorial species the sightline breaks it needs. Surface access for air-breathing must be maintained at all times.
Betta lehi can be kept as a pair or in a species-only setup. Males may be aggressive toward one another; a large, well-planted tank with visual barriers is required to house multiple males. The species is best kept with minimal tankmate pressure; small, peaceful fishes that share its water-chemistry requirements and do not compete aggressively for food or territory are the safest companions.
Conservation
Betta lehi has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). However, as a habitat specialist endemic to a small area of northwestern Borneo, it faces the same pressures affecting the region's freshwater fauna broadly: large-scale conversion of peat-swamp forest to oil-palm plantation, logging, drainage of wetlands, and associated water-quality degradation. Peat swamps in Sarawak and Kalimantan have been cleared and drained at scale over recent decades, and the highly specialised chemical conditions of intact peat swamps — low pH, near-zero dissolved solids, dense organic matter — cannot be replicated by secondary or degraded habitat.
The species' range straddles the Malaysia–Indonesia border, meaning its protection depends on land-use policies in two jurisdictions. No dedicated conservation programme is known for Betta lehi specifically. Hobbyist interest in wild bettas, when channelled into captive-breeding programmes, can maintain viable ex-situ populations independently of the wild, and specialist betta societies have played a meaningful role in sustaining knowledge and breeding stock of range-restricted species. The degree to which wild populations of Betta lehi are currently impacted by collection pressure relative to habitat loss is not well documented.