Taxonomy & naming
Betta brownorum was formally described by Witte and Schmidt in 1992, in the journal Ichthyological Exploration of Freshwaters (volume 2, issue 4, pages 305–330), under the full title 'Betta brownorum, a new species of anabantoids (Teleostei: Belontiidae) from northwestern Borneo.' The paper included a revised key to the genus. Eschmeyer's Catalog of Fishes (Catalog of Fishes, California Academy of Sciences) treats Betta brownorum Witte & Schmidt, 1992 as the valid name; because the species was described within Betta from the outset, the authority is written without parentheses.
The species belongs to the coccina group — a complex of small, darkly coloured, bubble-nesting wild bettas from the peat swamps and blackwater streams of Sundaland. Other members of the group include Betta coccina, B. tussyae, B. persephone, and B. miniopinna, all united by their red-to-maroon colouration, bubble-nesting behaviour, and dependence on extremely soft, acidic blackwater. Within the group, B. brownorum is distinguished by details of coloration and meristics documented in the original description.
Morphology
Betta brownorum is a very small fish, reaching approximately 1 in standard length (SL) according to FishBase; some hobby sources report specimens approaching 1.5–2 in total length under captive conditions, with the International Betta Congress noting up to 2.5 in, though wild-caught individuals are typically near the smaller end of that range. It is a slender, elongate betta with the rounded caudal fin and relatively short fins typical of the coccina group.
The body is deep reddish-brown to brick-red with a strong iridescent blue-green sheen on the scales that intensifies in displaying males and under directed light. A dark lateral stripe may be visible along the flanks depending on mood and light angle. The gill covers often display a bright iridescent blue-green spot. Females are generally duller, browner, and slightly smaller than males, lacking the full intensity of the male's iridescent sheen — though in the coccina group, sexual differences are more subtle than in the more familiar domesticated betta.
Habitat
Betta brownorum is a stenotypic peat-swamp specialist, meaning it is essentially unable to survive outside the very specific blackwater conditions of coastal peat-swamp forest. Its range spans the peat-swamp systems of Sarawak (Malaysian Borneo) and adjacent West Kalimantan (Indonesian Borneo) — a landscape of shallow, tannic, almost mineral-free water filtered through deep accumulations of organic peat.
The water chemistry of these habitats is extreme: pH values of 3–4 are typical, conductivity is negligible (dissolved mineral load near zero), and the water is deeply coloured by humic and fulvic acids leached from the peat. Temperatures in shaded peat-swamp forest run between 22 and 79 °F. The fish inhabit very shallow zones — puddles, ditches, and marginal pools at the forest edge — often only a few centimetres deep. As a labyrinth fish, B. brownorum breathes atmospheric air via the suprabranchial organ, making the extremely hypoxic, stagnant water of peat swamps habitable for it where most other fish cannot persist.
Feeding
In the wild, Betta brownorum is a micro-predator of small arthropods. Seriously Fish documents a diet dominated by ants, mites, and other small terrestrial invertebrates that fall onto the water surface — an opportunistic feeding strategy well suited to shallow, forested peat-swamp pools where surface insects are the main prey available. Aquatic invertebrates are also taken.
In captivity the species accepts small live and frozen invertebrate foods readily: Daphnia, freshly hatched Artemia nauplii, micro-worms, and small bloodworm are all reported as accepted. The fish's tiny mouth means that food size is important — only the smallest grades of food are appropriate. Dry foods may be taken but the species fares better on a live or frozen diet that more closely mirrors the invertebrate prey of its home swamps.
Mating
Betta brownorum is a bubble-nester. Males construct a raft of mucus-bound air bubbles, typically beneath a broad floating leaf or other surface cover at the water's surface, and defend this nest site against rivals. Courtship involves the male displaying intensely — spreading fins, intensifying body colour, and swimming alongside and around the female to assess her receptivity.
When a female is ready to spawn she signals passivity or approaches the nest site. The pair embrace in the classic anabantoid spawning clasp beneath or near the nest, with the male wrapping his body around the female and fertilising the eggs as she releases them. The eggs are buoyant and are gathered into the bubble nest by the male as they are released. The International Betta Congress notes that under certain circumstances B. brownorum has been observed to mouth-brood, though bubble-nesting is the primary and typical reproductive mode for the species.
Breeding
The male takes on full parental responsibility after spawning, guarding the bubble nest and retrieving any eggs or early larvae that sink from it. The female is typically removed after spawning to avoid predation of eggs by her or aggression from the guarding male. The male tends the nest until the fry become free-swimming, after which his role diminishes and he should also be separated to protect the brood.
The extremely soft, acidic water conditions of the natural habitat should be replicated for successful breeding: pH in the range of 3–4.5, very low or zero mineral hardness, and temperature around 75–79 °F. A layer of floating plants or broad surface leaves such as Indian almond (Catappa) leaves helps replicate the shaded peat-swamp surface and encourages nest building. Fry are very small at first and require infusoria or other micro-foods before advancing to baby brine shrimp and micro-worms.
In the aquarium
Betta brownorum is a specialist fish that demands soft, acidic blackwater conditions and will not thrive — let alone breed — in neutral or alkaline tap water. Peat filtration, reverse-osmosis water, or rain water adjusted with botanical additives (dried Catappa leaves, alder cones) is used to achieve the species' required chemistry: pH 3–4.5, negligible hardness, temperature 72–79 °F. A soft substrate and dim lighting with floating plants mimicking the forest canopy suit the species' retiring nature.
Because of its small size, B. brownorum is best kept in a species-only or very carefully chosen community of similarly sized, soft-water fishes. Males may be territorial toward one another; a small, well-planted tank for a single pair or small group with dense cover is typical practice. As a labyrinth fish it requires access to the water surface to breathe atmospheric air — a tight-fitting lid is essential both to ensure humid air above the water (cold draughts can damage the labyrinth organ) and to prevent the excellent jumper from escaping. Filtration should be very gentle to preserve the still, stagnant conditions the species prefers.
Conservation
Betta brownorum is assessed as Vulnerable (VU) on the IUCN Red List. The species' dependence on intact peat-swamp forest places it in one of the most heavily threatened habitat types in Southeast Asia. Lowland peat swamps across Borneo have been drained, burned, and converted to oil palm and other agricultural use at an accelerating rate over recent decades, eliminating both the habitat structure and the extreme water chemistry on which the species depends.
The species' restricted range — a relatively narrow zone of coastal peat swamp in Sarawak and West Kalimantan — means that even localised habitat loss can affect a significant fraction of the total population. Collection for the ornamental fish trade represents an additional pressure on wild populations, though the species is bred in captivity by specialist hobbyists and betta enthusiasts. Supporting habitat protection initiatives in Borneo and sourcing captive-bred specimens are the two most direct actions available to aquarists who keep the species.