Taxonomy & naming
Betta spilotogena was described by Peter K. L. Ng and Maurice Kottelat in 1994 in a revision of the Betta waseri species group published in the Raffles Bulletin of Zoology (42(3): 593–611). The type locality is a small stream north of Bintan Island, Riau Archipelago, Indonesia. Eschmeyer's Catalog of Fishes (Catalog of Fishes) records the valid name as Betta spilotogena Ng & Kottelat, 1994.
The species belongs to the waseri group, a clade of larger paternal mouthbrooders within the genus Betta distributed across the Malay Peninsula and the western Indonesian archipelago. The waseri group is characterised by the mouthbrooding reproductive mode and by a suite of morphological characters separating them from the smaller bubble-nesting species. B. spilotogena is one of the island-endemic members of the group, recorded only from Bintan and Singkep in the Riau Islands.
The specific epithet spilotogena is derived from the Greek spilos (spot or stain) and gena (cheek), referring to the spotted or mottled pattern on the head and opercular region that distinguishes this species from its closest relatives in the waseri group.
Morphology
Betta spilotogena is a medium-sized wild betta, reaching approximately 3 in standard length according to FishBase, with Seriously Fish noting a maximum of 2.5–3 in SL. Like other waseri-group bettas it has a robust, moderately elongated body and a broad, somewhat rounded head. Males develop broader heads and more elaborate finnage than females, and are more intensely coloured, particularly during display and courtship.
The colour pattern includes the mottled or spotted cheek markings that give the species its name, set against a body that shows iridescent blue-green or teal scales on the flanks, with reddish or brownish tones overlaid. Unpaired fins are typically rounded to lanceolate in males, with colouration that may include red, blue, or dark pigmentation depending on the individual's state and lighting. As in all members of the genus Betta, B. spilotogena possesses a suprabranchial labyrinth organ that allows it to breathe atmospheric air directly, an adaptation to the low-oxygen conditions of its swamp habitat.
Habitat
Betta spilotogena is known from freshwater swamps and associated forest streams on Pulau Bintan and Pulau Singkep in the Riau Islands, Indonesia. The species occupies shallow water, typically less than 3 ft in depth, with dense riparian and emergent vegetation providing cover. The type locality is described as a small stream north of Bintan Island.
Water conditions recorded at the known localities are clear to lightly tannin-stained, soft, and strongly acidic — characteristic of the peat-swamp environment of the lowland Sunda shelf islands. Seriously Fish documents temperature 72–81 °F, pH 4.0–6.5 (measured 4.9–5.5 at collection sites), and hardness 0–90 ppm. These are the blackwater conditions typical of peat-dome swamps: low mineral content, high dissolved organic carbon from decomposing vegetation, and very low conductivity.
The labyrinth organ is a critical adaptation here: peat-swamp water is often near-anoxic in still sections, and the ability to gulp air at the surface allows the fish to thrive where dissolved-oxygen levels would exclude obligate gill-breathers. Dense overhanging vegetation and a heavy leaf litter beneath shallow water define the microhabitat.
Feeding
In nature, Betta spilotogena is an opportunistic carnivore, feeding on small insects, invertebrates, and zooplankton encountered at or near the water surface and in the water column. This is consistent with the feeding ecology of other wild bettas in forest-swamp habitats, where terrestrial and semi-aquatic invertebrates falling onto the water surface are an important food source.
In captivity the species accepts a range of small live and frozen foods readily — Daphnia, Artemia (brine shrimp), bloodworm (chironomid larvae), and similar items. Seriously Fish notes that it will take appropriately sized live and frozen invertebrate foods in the aquarium. A diet centred on live and frozen invertebrates rather than dry prepared food is more consistent with its natural diet and maintains condition and colour better.
Mating
Betta spilotogena is a paternal mouthbrooder, a reproductive mode shared by all members of the waseri species group. Courtship involves the male displaying to the female with spread fins and intensified colouration; the characteristic embrace of Betta — in which the male wraps his body around the female during spawning — results in the release and fertilisation of eggs.
Males of waseri-group bettas are notably less aggressive toward conspecifics compared to the bubble-nesting fighting fishes, though territorial behaviour during breeding remains pronounced. The male's broader head is associated with the mouthbrooding function: a large buccal cavity accommodates the developing eggs and larvae. Seriously Fish notes that the species can be maintained in pairs or small groups outside of breeding, though community tanks are not recommended given its specific habitat and dietary requirements.
Breeding
After the spawning embrace, the fertilised eggs are collected by the male and held in his buccal cavity. The incubation period is approximately 10–21 days, during which the male does not feed. The eggs develop through larval stages within the mouth, and the fry emerge free-swimming after the male releases them. The extended incubation range likely reflects temperature dependence, with warmer water shortening the period.
In the aquarium, breeding B. spilotogena follows the pattern of other waseri-group mouthbrooders. A conditioned pair introduced to a well-planted, dimly lit tank with soft, acidic water consistent with the species' natural range of pH 4.0–6.5 and temperatures of 75–81 °F is the standard approach. Once the male is holding, he should not be disturbed; some breeders isolate the holding male or allow him to release fry into the breeding tank, removing him afterward. Fry are relatively large compared to those of bubble-nesting bettas and can take newly hatched brine shrimp from the outset.
In the aquarium
Betta spilotogena is an infrequently seen species in the hobby, appearing occasionally in specialist wild-betta circles. Its care requirements are more demanding than those of the common Siamese fighting fish: it needs soft, acidic water (pH 4.0–6.5, hardness as low as possible), temperatures of 72–81 °F, and a quiet, well-planted aquarium with minimal water movement. As a labyrinth fish it must have unobstructed access to the water surface to breathe air; the space between the water surface and the tank lid should be kept warm and humid to avoid chilling the labyrinth organ.
A species-only or conspecific setup is strongly preferred. Gentle filtration — sponge filters are ideal — keeps the water clean without generating currents the fish finds stressful. Heavily planted tanks with leaf litter on the substrate approximate the tannin-stained, shaded swamp habitat and also help buffer the pH naturally. Peat filtration or the use of botanicals (seed pods, dried leaves) can help maintain the low pH and soft-water conditions the species requires.
Availability is limited; most individuals in the hobby originate from specialist breeders. Given the species' Endangered status and the ongoing destruction of its peat-swamp habitat, captive-bred specimens are strongly preferred over wild-caught fish.
Conservation
Betta spilotogena is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), assessed on 7 January 2019. The listing reflects a restricted extent of occurrence combined with continuing decline in the area, extent, and quality of its peat-swamp habitat. The species' entire known range is confined to two islands in the Riau Archipelago — Bintan and Singkep — making it highly vulnerable to any localised habitat loss.
The primary threat is the large-scale drainage, burning, and conversion of lowland peat swamps across the Riau Islands for plantation agriculture, particularly oil palm and acacia pulpwood. This process has been ongoing for decades and has destroyed a substantial proportion of the original peat-swamp extent in the region. The IUCN assessment records a status change from Vulnerable (2018) to Endangered (2019) driven by improved information rather than a sudden decline, suggesting the historical assessment underrepresented the degree of threat.
No specific conservation measures targeting B. spilotogena are documented. The species' persistence depends on the survival of intact lowland peat-swamp forest on its island range, an ecosystem under severe and continuing pressure. Aquarists keeping and breeding the species in captivity contribute to maintaining a population outside the wild, though no formal ex-situ conservation programme is known to exist for this species.