Taxonomy & naming
Betta chini was formally described by Peter K. L. Ng in 1993 in the journal Ichthyological Exploration of Freshwaters (volume 4, number 4, pages 289–294). The type material was collected from peat swamps in Sabah, Malaysian Borneo, and the species is placed in the akarensis group of the genus Betta — a clade of mouthbrooding bettas distributed across Borneo and parts of the Sunda shelf. Eschmeyer's Catalog of Fishes (Catalog of Fishes, California Academy of Sciences) records the valid name as Betta chini Ng, 1993.
The specific epithet chini is a patronym honouring the collector of the type series; the name follows the standard latinisation used for such dedications in ichthyological nomenclature. Within the akarensis group, B. chini is characterised by a suite of meristic and morphometric features described in the original account and elaborated by Kamal et al. (2020) from a 2019 Klias Forest Reserve series: an interrupted postorbital stripe on the opercle, a vivid yellow eye in life, anal-fin ray counts of 26–30 (mode 28), lateral scale counts of 30–31 (mode 31), and a notably long anal-fin base (54.8–58.5% of standard length). These characters collectively separate it from its akarensis-group congeners, including the closely related B. nuluhon described from Sabah by Kamal et al. in 2020.
Morphology
Betta chini is a moderately sized betta reaching approximately 2 in standard length in adults; FishBase records males to 2 in SL and females slightly larger at up to 2 in SL. The body is stocky with a convex dorsal profile, a shape consistent across the 2019 Klias series and noted by Kamal et al. as a characteristic of the species. Some specimens from that series reached 2.5 in SL, exceeding the maximum recorded in Ng's original type series (2 in SL).
The opercle carries an interrupted postorbital stripe — a diagnostic feature within the akarensis group. In live fish the iris is yellow, a readily observed field character. The anal fin is proportionally long, with its base spanning more than half of standard length, and ray counts range from 26 to 30 (mode 28). Subdorsal scales number 5½–7 (mode 6); predorsal scales 22–24 (mode 23); postdorsal scales 9–11 (mode 10). Coloration in life has not been extensively documented in the primary literature, but as an akarensis-group member the species likely displays the muted brown and iridescent blue-green lateral banding typical of the clade, intensifying in displaying males. Sexual dichromatism is present but not strongly documented; females in mouthbrooding bettas are generally less colourful than males and may be slightly larger in some species.
Habitat
Betta chini inhabits shallow peat-swamp forest in the lowlands of Sabah, Malaysian Borneo. The IUCN assessment records two confirmed populations: the peat swamp forests of the Klias Peninsula (centred on Beaufort and Klias Forest Reserve) and a hillstream near Babagon in Penampang district. The species is benthopelagic and found in very shallow water — typically less than 2 ft — over substrates of leaf litter, woody detritus, and peat. The surrounding forest is primary or degraded peat-swamp forest.
Like all peat-swamp specialist bettas, B. chini lives in blackwater: water coloured dark amber to brown by dissolved humic and fulvic acids leaching from the peat and decaying vegetation. Such water is typically very soft, highly acidic (pH well below 7), extremely low in dissolved minerals, and poor in dissolved oxygen — conditions that are precisely why the labyrinth organ evolved in anabantoids. Surface access is essential, as the fish supplements gill respiration with atmospheric air breathed directly at the surface. Still or near-still water, dense leaf litter, and the structural complexity of submerged roots and fallen timber characterise the microhabitat.
Feeding
No detailed dietary study of Betta chini in the wild has been published. As a small carnivore typical of the genus, it almost certainly preys on invertebrates available in the peat-swamp environment: small insects and their larvae, microcrustaceans, worms, and other soft-bodied invertebrates encountered in the leaf litter and at or near the water surface. The shallow, densely vegetated blackwater environment is relatively impoverished in large prey, and bettas at this size class tend toward opportunistic ambush feeding rather than active pursuit.
In captivity, akarensis-group bettas are generally accepted to take live and frozen small invertebrates (Daphnia, brine shrimp, chironomid larvae, small earthworm pieces), and quality small pellets or micro-pellets are accepted by acclimatised individuals. Live foods are preferred, particularly for conditioning prior to breeding, and a diet rich in varied invertebrate matter supports both colour development and reproductive readiness. As with all small mouthbrooding bettas, overfeeding and poor water quality are risks to avoid.
Mating
Betta chini is a paternal mouthbrooder, as are all members of the akarensis group. Courtship follows the pattern typical of mouthbrooding Betta: the male displays intensely to the female, spreading fins and intensifying body colouration to signal condition and dominance. The pair engage in close body-contact circling before spawning embraces begin. During each embrace the female releases a small number of eggs, which are fertilised externally; eggs and milt fall together.
Following the embrace the male collects the fertilised eggs into his buccal cavity. This is the defining moment of the mouthbrooding mode: rather than constructing a bubble nest and tending eggs externally, the male takes direct physical custody of the clutch. In practice, akarensis-group spawning involves a series of repeated embraces over an extended period until the female has released her full complement of eggs. The male's buccal cavity holds the entire clutch, and he ceases feeding for the duration of the incubation period.
Breeding
After collecting the fertilised eggs, the male Betta chini broods the clutch in his mouth for approximately ten days (FishBase gives this figure for the species, noting it is assumed equivalent to the closely related B. picta). During this period the male eats nothing; the buccal cavity provides both mechanical protection and presumably some degree of aeration from the male's own respiratory movements. Incubation conditions in the blackwater peat swamp — warm, soft, and acidic — are presumably what the species is adapted to replicate.
At the end of the incubation period the male releases the free-swimming fry, which are relatively well-developed at this stage compared with the hatchlings of egg-scattering species. Clutch sizes in the akarensis group are typically modest — a reflection of the higher parental investment per offspring in mouthbrooding — and the fry are correspondingly larger at release. In captivity, breeders of related akarensis-group species recommend maintaining the brooding male in a quiet, stress-free environment and offering the fry appropriately sized live foods (Artemia nauplii, Paramecium, or fine-ground dry foods) once released. The male should not be disturbed during brooding, as stress may cause him to swallow or expel the clutch prematurely.
In the aquarium
Betta chini is an uncommon species in the aquarium hobby and is seldom encountered outside specialist betta circles. Its care requirements reflect its blackwater peat-swamp origins closely: the species does best in soft, acidic water with low conductivity and low pH (pH 4.5–6.5 is appropriate for akarensis-group bettas), gentle or near-absent flow, and warm temperatures in the range typical of Sabah lowland habitats. Tannin-rich water conditioned with botanicals (dried leaves, alder cones, catappa extract) replicates the blackwater chemistry and is strongly recommended. Surface access is non-negotiable — as a labyrinth fish it must be able to breathe atmospheric air, and a tight-fitting lid is advisable both to retain humidity above the water surface and to prevent jumping.
As a relatively small, shy species it should be kept away from boisterous or aggressive tankmates. A species tank or a quiet biotope setup with conspecifics or very peaceful, similarly sized fishes is most appropriate. Dense planting and a thick layer of leaf litter on the substrate give the fish cover and mimic the natural habitat structure; subdued lighting suits both the fish and the aesthetic of a peat-swamp biotope. Given its Endangered status, sourcing captive-bred animals from reputable specialist breeders is strongly preferable to any wild-caught stock, and participation in a breeding programme is a meaningful contribution to the species' captive continuity.
Conservation
Betta chini is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), based on an assessment by B. W. Low published in 2019. The extent of occurrence is just 77 mi², and the species is known from only two threat-defined locations: the Klias Peninsula peat swamps and the Babagon hillstream area in Penampang. Population trend is listed as unknown. The primary threats are habitat conversion to forestry plantations and monoculture agriculture, logging, and fire; the catastrophic fires of the 1998 El Niño event burned extensively across the Klias Peninsula peat swamps, which represent the core of the species' known range. Kamal et al. (2020) confirmed that a viable population still persisted in the Klias Forest Reserve in 2019, but the surrounding habitat remains heavily degraded.
No specific conservation actions are recorded as being in place for the species. The Klias Forest Reserve provides some degree of formal protection to part of the habitat, but peat swamps in Malaysian Borneo face ongoing pressure from agricultural expansion, drainage, and the persistent risk of fire. The extremely small extent of occurrence and the limited number of known localities mean that any further large-scale disturbance — particularly fire — could be catastrophic for the species. Listing in relevant trade monitoring frameworks and targeted field surveys to locate additional populations would be meaningful first steps toward a more complete conservation strategy.