Taxonomy & naming
Betta hendra was described by Ingo Schindler and Horst Linke in 2013 in the journal Vertebrate Zoology (63(1):35–40), based on specimens collected from the Sabangau peat-swamp forest approximately 2 mi south-east of Palangkaraya, Kalimantan Tengah, on the island of Borneo. The type locality lies within the Sungai Sebangau drainage, a blackwater river system draining one of the largest remaining lowland peat-swamp forests in Southeast Asia. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) recognises Betta hendra Schindler & Linke, 2013 as the valid name.
The species belongs to the coccina group, an assemblage of small bubble-nesting bettas distributed across the Sunda shelf that share a preference for blackwater and peat-swamp habitats and are characterised by rich red, green, and blue iridescence. Within this group, Betta hendra was collected in sympatry with Betta foerschi during the type survey of May 2011, which confirms that the two species can co-occur in the same reach of swamp without obvious competitive exclusion. The coccina group has been subject to ongoing revision as molecular and morphological studies refine species boundaries across Sundaland.
Morphology
Betta hendra is a small betta reaching approximately 1–2 in standard length, with FishBase recording a maximum of 1.5 in SL. The body form is typical of the coccina group: slender and slightly laterally compressed, with the rounded finnage and relatively small caudal fin characteristic of bubble-nesting bettas rather than the elaborate trailing fins of domesticated strains.
Sexual dimorphism is moderate. Males are the more vivid sex, displaying bright iridescent green scaling across the flanks and fins with dark, well-defined opercular bars — the latter a key diagnostic character within the coccina group. Females are plainer and lack the intensity of the male's iridescence. The combination of green iridescence and strong opercular barring distinguishes Betta hendra from its closest relatives in the group, though precise identification of coccina-group members benefits from comparative material and locality data.
Habitat
Betta hendra inhabits the shallow, still, heavily shaded interior of peat-swamp forest in the Sungai Sebangau drainage of Kalimantan Tengah. Field surveys at the type locality recorded water depths of only 2–19.5 in, with no measurable current, dense riparian vegetation, and a closed forest canopy reducing light penetration to the forest floor. This is the archetypal Sundaland blackwater micro-habitat: water stained dark brown by dissolved humic and fulvic acids leached from the deep peat substrate.
Water chemistry at the type locality was extreme by any standard: pH 4.0, conductivity a mere 6 μS/cm, and temperature 83 °F at the time of collection. These figures capture what hobbyists mean when they speak of blackwater — not merely soft and acidic, but essentially ion-free water of near-distilled purity. Like all members of the genus, Betta hendra is a labyrinth fish and breathes atmospheric air directly through its suprabranchial organ, an adaptation that suits it to the oxygen-depleted, still-water conditions prevalent in peat swamps.
Feeding
In nature, Betta hendra is an insectivore and small-invertebrate predator, taking insects and other small invertebrates that fall onto or live near the swamp surface. The species hunts in the shallow, still water layer where terrestrial invertebrate input from the overhanging riparian vegetation is concentrated.
In the aquarium, the species accepts live and frozen foods readily: Daphnia, Artemia nauplii and adults, bloodworm, and similar small invertebrate prey are all taken. Conditioning adults for breeding on live or high-quality frozen foods is strongly recommended, as the species' response to flake or pellet-based diets alone can be variable. Feeding small amounts frequently suits the fish's hunting style and the limited stomach capacity of a 1.5 in predator.
Mating
Betta hendra is a bubble-nester. The male constructs a floating raft of mucus-bound air bubbles, typically anchored beneath a broad leaf or other surface feature at the water's surface, and the nest serves as the focal point of courtship. Males in breeding condition develop heightened iridescence and display lateral flaring and fin erection toward rival males and toward receptive females.
Courtship involves the male drawing the female toward the nest through a series of displays and short chases. The species is reported to be peaceful and can be maintained in small groups or pairs in a sufficiently large, well-planted enclosure, though males will spar with one another and benefit from broken lines of sight. Behaviour consistent with the broader coccina group suggests that pair bonds are relatively tight during the spawning period, with the male taking the dominant role in both courtship and subsequent nest tending.
Breeding
Once courtship is complete, the pair spawns in a brief embrace beneath the bubble nest. Eggs are released and fertilised, then collected by the male in his mouth and blown into the nest. Clutch sizes are modest: typical spawnings produce fewer than 20 eggs, though up to approximately 50 have been reported. Eggs hatch within 24–72 hours, and the fry become free-swimming after a further 3–4 days, at which point the male's parental role diminishes.
Breeding requires the maintenance of blackwater conditions or close approximations: very soft, acidic water (pH 4.0–6.5, hardness 18–90 ppm in the range Seriously Fish cites for aquarium husbandry) and warm temperatures in the range 72–81 °F as recommended for captive care. The male guards the nest throughout incubation; disturbance during this period can cause nest abandonment. Rearing fry requires extremely small first foods — infusoria or similar microorganisms — given the tiny size of newly free-swimming individuals from a species reaching only 1.5 in at adulthood.
In the aquarium
Betta hendra is an exacting species for the specialist rather than a beginner. Its strict requirement for soft, hyper-acidic blackwater — ideally with pH in the 4–6 range, negligible hardness, and the low conductivity characteristic of peat-swamp water — means that ordinary tap water prepared with standard conditioners will not suffice. Reverse-osmosis water remineralised to very low TDS, or water passed through a peat column and conditioned with Indian almond (Catappa) leaves, more closely mimics the species' natural chemistry.
The aquarium should be small (species tanks of 10–15 US gal are appropriate), densely planted or furnished with floating vegetation and leaf litter, dimly lit, and equipped with only the gentlest of filtration — a sponge filter running at low output is typical, since the species lives in still water and the bubble nest is easily disrupted by surface turbulence. Access to a humid air layer above the water surface is essential for a labyrinth fish. Tankmates should be absent or restricted to other small, non-aggressive species of compatible water-chemistry requirements. The species is peaceful but retiring and will be outcompeted at feeding by boisterous companions. Most stock in the hobby is collected or bred by specialists; sourcing captive-bred individuals reduces pressure on wild populations and typically yields healthier, more adaptable fish.
Conservation
Betta hendra is assessed as Critically Endangered (CR) on the IUCN Red List (assessed 12 January 2019, criterion B2ab(iii)), a status that reflects both the extent and rate of habitat loss across its range. The Sungai Sebangau peat-swamp forest — the entirety of the species' known range — is under severe ongoing pressure from drainage for agricultural conversion, fire, and logging. Borneo's peat-swamp forests have contracted dramatically in recent decades, and the hydrological conditions that maintain them — a permanently saturated, deep peat layer — are destroyed rapidly and essentially irreversibly once drainage ditches are cut.
The threat is compounded by collection for the ornamental fish trade. Betta hendra's attractiveness to aquarists and its restricted range have made it a target for wild collection, and a 2023 emergency petition under the US Endangered Species Act documented both habitat degradation in the Sabangau forest and ongoing harvest pressure as grounds for listing consideration. The species' entire known range falls within a single drainage system, leaving no buffer population to sustain recovery if the primary habitat is lost. Captive breeding by specialist keepers represents the most meaningful contribution the aquarium hobby can make to the species' prospects.