Taxonomy & naming
Betta patoti was formally described by Max Weber and Lieven Ferdinand de Beaufort in 1922, based on material collected from the southern part of Kalimantan Timur (East Kalimantan), Indonesian Borneo. The type locality is the Mangar River, approximately 16 mi from Balikpapan City. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Betta patoti Weber & de Beaufort, 1922, and the species has remained in the genus Betta without major taxonomic revision.
Betta patoti belongs to the unimaculata group, a clade of large, mouthbrooding bettas distributed across Borneo and parts of peninsular Southeast Asia. Members of this group share the paternal mouthbrooding reproductive strategy and tend toward greater body size than the bubble-nesting members of the genus. The species epithet patoti commemorates W.J. Tissot van Patot, a collector who worked in the Dutch East Indies and whose specimens contributed to early knowledge of Bornean freshwater fishes.
Morphology
Betta patoti is one of the larger members of the genus, with males reaching up to 4 in total length (FishBase) and some sources citing up to 5 in (5 in) for well-grown individuals. The body is elongated and robust compared with smaller Betta species, with rounded fins typical of the mouthbrooding bettas rather than the elaborate finnage of domesticated Betta splendens.
Coloration varies markedly by locality. Populations around Balikpapan tend toward a blackish ground colour with prominent dark vertical bars — the pattern that earned the species its occasional common name 'Tiger Betta'. Northern populations in Kutai Kartanegara Regency show more reddish tones, while fish collected near Samarinda display a greenish iridescent sheen. This geographic colour variation is typical of the unimaculata group and makes wild-caught provenance relevant to accurate identification. Sexual dimorphism is minimal compared with bubble-nesting bettas; females tend to be slightly smaller and plainer, but the difference is not pronounced.
Habitat
Betta patoti inhabits blackwater streams and rivers in the lowland forests of southern East Kalimantan, Indonesia. The species' documented range extends from the Mangar River drainage near Balikpapan northward into Kutai Kartanegara Regency. Seriously Fish reports that water chemistry at the type locality is markedly soft and acidic (pH 4, GH 179 ppm — the very low GH figure confirms extremely soft water rather than contradicting the low pH), characteristic of the tannin-stained, humus-laden blackwater systems that percolate through lowland Bornean peat and forest soils.
FishBase records a broader pH tolerance of 5.5–6.8 for the species and temperatures of 73–82 °F, likely reflecting the range across multiple collection sites rather than a single locality. Like all Betta, B. patoti is a labyrinth fish capable of breathing atmospheric oxygen directly via the suprabranchial organ, an adaptation that allows it to survive the low dissolved-oxygen conditions typical of warm, still, or slowly flowing blackwater environments. The species appreciates some water movement in parts of its range, consistent with its occurrence in stream rather than purely stagnant habitats.
Feeding
Betta patoti is a carnivore in nature, feeding on insects, small invertebrates, and zooplankton encountered at or near the water surface and in the water column. The species' relatively large size and the robust build of wild-caught adults suggest it can take larger prey items than smaller Betta.
In aquaria the species accepts a varied diet including sinking granules, floating cichlid pellets, fish flakes, and frozen or fresh foods such as bloodworm, Daphnia, brine shrimp, and earthworms. Tropical Fish Hobbyist recommends a fasting day once per week to maintain digestive health, a practice common with predatory labyrinth fishes kept at size. Offering live and frozen foods alongside dried staples improves body condition and breeding readiness.
Mating
As a member of the unimaculata group, Betta patoti is a paternal mouthbrooder. Courtship involves the male displaying to the female, and spawning takes place in a characteristic embrace near or at the bottom of the tank or stream substrate. During the embrace the male wraps around the female and fertilises the eggs as they are released.
After spawning, the male collects the fertilised eggs into his buccal cavity. Tropical Fish Hobbyist notes that males appear to distinguish between fertile eggs (which develop into embryos) and infertile nutrient eggs, and that inexperienced males may require several spawning attempts before effectively retaining and incubating a full clutch. Clutches of up to 80 eggs have been reported. The female takes no role in egg or fry care once spawning is complete.
Breeding
The male incubates the fertilised eggs orally for approximately 14 days, eating nothing throughout the brooding period. This extended fast is physiologically demanding, and males should be offered abundant food both before spawning and after releasing the fry. Once the fry are sufficiently developed — typically as free-swimming miniatures with functional labyrinth organs forming — the male releases them, at which point they must fend for themselves and should generally be separated from the adults.
Water chemistry for breeding does not need to be as extreme as for some mouthbrooding bettas that require pH values below 4; Tropical Fish Hobbyist notes that B. patoti tolerates a more neutral pH with moderate hardness for successful spawning, though softer and more acidic conditions mimicking the natural blackwater habitat are likely to reduce stress and encourage more reliable conditioning. The soft, dimly lit tank setups favoured for blackwater bettas — tannin-stained water, leaf litter, subdued lighting — suit this species both for spawning and for rearing the released fry.
In the aquarium
Betta patoti is kept by specialist hobbyists interested in wild Betta species and the mouthbrooding groups in particular. Its larger size relative to most bettas — approaching 4.5 in in mature males — means it requires a more spacious setup than is typically envisaged for the genus: a tank of 31.5 in or more in length is appropriate for a pair or small group. A well-fitted lid is essential, as all Betta are capable jumpers.
The species appreciates a setup that replicates its blackwater habitat: soft, acidic water conditioned with peat or dried leaves, gentle filtration that provides some flow without strong turbulence, and dim or diffuse lighting. Botanicals such as Indian almond leaves both tint the water beneficially and provide cover. Tropical Fish Hobbyist notes the species is not overly aggressive toward dissimilar tankmates but should not be kept with very small fish that could be viewed as prey. Pairs or a single male with one or two females can be kept together; multiple males are best avoided unless the tank is large and heavily structured. Surface access must be unobstructed at all times so the fish can gulp atmospheric air.
Conservation
Betta patoti is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), assessed 28 December 2018. The Endangered listing reflects a restricted extent of occurrence combined with documented or inferred declines in habitat quality within the species' East Kalimantan range. The lowland forests and blackwater stream systems of southern and central Kalimantan have faced severe pressure from logging, agricultural conversion — particularly oil palm expansion — and associated drainage alteration and siltation, all of which degrade the soft, acidic, shaded stream habitat on which this species depends.
The limited geographic range amplifies the species' vulnerability: there is no large outlying population buffering against local declines. Collection for the ornamental trade has historically been a supplementary pressure, though the species is uncommon in international commerce. Conservation of B. patoti depends on the retention of structurally intact lowland forest and its associated blackwater drainage network across East Kalimantan, a region that has experienced some of the highest deforestation rates in Indonesia over the past three decades.