Taxonomy & naming
Betta strohi was described by Schaller and Kottelat in 1989, with type localities in the Jelai, Mentaya (Sampit), Sebangau, and Kahayan river basins of Borneo — a spread of blackwater drainages across the central and southern part of the island in the Indonesian province of Kalimantan. Eschmeyer's Catalog of Fishes records the valid name as Betta strohi Schaller & Kottelat, 1989.
The species belongs to the foerschi group, a cluster of paternal mouthbrooding Betta characterised by iridescent blue or green unpaired fins and a pale or white distal band on the dorsal fin. The foerschi group sits within the much larger genus Betta, which spans both bubble-nesting and mouthbrooding clades and encompasses well over 70 described species across Southeast Asia. Within the group, B. strohi is most likely to be confused with its swamp-dwelling relatives where ranges are proximate, and careful attention to distribution records and fin patterning is needed when identifying preserved or traded specimens.
Morphology
Betta strohi is a slender, moderately elongate species reaching a maximum of around 3 in total length, with most individuals in the 2.5–3 in range. The body plan is typical of the foerschi group: a relatively pointed snout, a slightly upturned mouth suited to surface feeding, and the rounded caudal fin characteristic of most wild mouthbrooding bettas.
Unpaired fins carry the iridescent blue-green coloration that defines the foerschi group, with a pale to white distal band on the dorsal — a shared character of the group that assists identification in the field and from photographs. Ground coloration of the body is brownish to olive, overlaid with iridescent scales that catch light differently depending on angle and mood. As in most wild bettas, fully ripe males are considerably more vivid than females, and colour intensity varies markedly with stress and reproductive state. The suprabranchial labyrinth organ is present and developed, as in all Betta.
Habitat
Betta strohi occupies blackwater peat-swamp forests and forest streams in central and southern Borneo, a habitat type defined by the slow percolation of rainfall through deep beds of decomposing plant matter. The resulting water is extraordinarily soft and acidic — pH typically 4.5–5.5, general hardness in the range of 4–12 dGH — stained brown by humic and fulvic acids and carrying almost no dissolved minerals. Dissolved oxygen is often low, a condition that makes the labyrinth organ essential: these fish breathe atmospheric air at the surface as well as extracting oxygen through the gills.
Physically, the habitat is characterised by very slow or stagnant flow, dense emergent and overhanging vegetation blocking much direct sunlight, and a substrate of saturated peat, submerged roots, fallen leaves, and waterlogged deadwood. Temperature ranges from roughly 72–84 °F. This is not a generalist's environment: the chemical and physical conditions are highly specific, and the species has evolved to exploit a niche that few other fish can tolerate.
Feeding
In nature, Betta strohi feeds primarily on small benthic and aquatic invertebrates — insect larvae, microcrustaceans, and other small organisms associated with the leaf-litter substrate — as well as insects taken from the water surface. The upturned mouth is well suited to surface prey capture, and the species is recorded as diurnal in its feeding activity.
In aquarium conditions the diet can be met with small live and frozen foods: Daphnia, Artemia nauplii, bloodworm, and small terrestrial insects such as fruit flies. Dried foods may be accepted over time but live and frozen items produce better condition and colour. Because the fish are territorial and may compete at feeding, care is needed to ensure subordinate individuals receive adequate food, particularly in a species tank with multiple males.
Mating
Betta strohi is a paternal mouthbrooder: after courtship and a spawning embrace, the fertilised eggs are taken into the male's mouth for incubation. Courtship involves the male displaying to the female with flared fins and spread gill covers, and the characteristic lateral posturing seen across the mouthbrooding bettas. The embrace itself is typical of the genus — the male wraps around the female, eggs and milt are released simultaneously, and the male collects the sinking eggs before they reach the substrate.
Males in the foerschi group are reported to sometimes accept small amounts of food during the brooding period — a departure from the strict fast observed in some other mouthbrooding Betta species. This may reflect the relatively extended incubation period and the energetic demands of prolonged oral incubation in a territorial fish. Females should be removed or given ample cover once spawning is complete, as males may harass them.
Breeding
Following spawning, the male holds the fertilised eggs in his buccal cavity for approximately 8–14 days, during which he is largely reclusive and should not be disturbed. The number of eggs per brood is small relative to egg-scattering species — typical of mouthbrooding bettas where parental investment per offspring is high. Water temperature within the breeding range (around 77–82 °F) influences incubation duration.
Fry released from the male's mouth are relatively large and well developed compared with the larvae of bubble-nesting species, and can accept microworm and Artemia nauplii as first foods immediately after release. Soft, acidic, tannin-rich water is strongly recommended for successful brooding and fry survival: attempting to breed this species in hard, neutral, or alkaline conditions substantially reduces success rates. The male should be given a quiet retreat — a cave, dense plant cover, or a section of broad-leafed plant against which to anchor — during the brooding period.
In the aquarium
Betta strohi is rare in the aquarium trade and held primarily by specialist breeders with an interest in wild Betta conservation. It demands water chemistry that closely mirrors its natural habitat: very soft (GH 4–12), strongly acidic (pH 4.5–5.5), and warm (77–82 °F). Peat filtration, Indian almond leaves, or driftwood are standard tools for achieving and maintaining the required chemistry and tannin load. A well-established, biologically mature aquarium is essential — this species does not tolerate instability.
The tank should replicate the low-light, slow-flow conditions of peat-swamp forest: subdued lighting, minimal surface agitation (while still allowing surface access for air breathing), and a heavy planting of floating and low-growing species. Leaf litter on the substrate provides both shelter and foraging substrate. Males are territorial toward one another and should generally be kept one per tank unless the aquarium is large enough to establish clear visual barriers. A species-only setup or a carefully chosen community of other blackwater specialists is the safest approach. As a labyrinth fish, a tightly fitting lid is essential — Betta are capable jumpers.
Betta strohi is noted as diurnal and can be observed actively feeding and displaying during daylight hours under appropriate conditions. Its rarity in the hobby means that maintaining and breeding captive groups has real conservation value, and fish sourced from established captive lines are greatly preferable to wild-caught individuals given the habitat pressures the species faces.
Conservation
Betta strohi has not been formally assessed by the IUCN Red List and currently carries a status of Not Evaluated (NE). However, the species' dependence on intact peat-swamp forest in Borneo places it in a habitat among the most imperilled on earth. Kalimantan's lowland peat swamps have been subject to large-scale drainage, burning, conversion to palm oil and timber plantations, and peatland fires over recent decades — pressures that have dramatically reduced and fragmented this habitat type across the island.
For a species with a restricted range tied entirely to this one habitat, undocumented does not mean secure: the absence of a formal IUCN assessment reflects data gaps, not evidence of population stability. Academic work on Betta bioecology has flagged conservation concern for peat-swamp Betta specialists on the basis of habitat trajectory alone. Specialist hobbyist breeding programmes that maintain captive populations of B. strohi provide a genuine buffer against continued wild habitat loss, and support for such programmes is the most direct contribution aquarists can make to the species' long-term survival.