Taxonomy & naming
Belontia signata was described by the German-British ichthyologist Albert Günther in 1861, based on specimens from what was then Ceylon (now Sri Lanka). The parenthetical authority reflects that Günther placed the species in a different genus from Belontia, which was erected later to receive it; Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises the valid name as Belontia signata (Günther, 1861).
The genus Belontia is a small Southeast Asian group within the family Osphronemidae, closely allied to the true gouramis and sharing their defining labyrinth organ. B. signata is the type species and the only member of the genus native to Sri Lanka; the closely related B. hasselti occurs in mainland Southeast Asia and the Malay Archipelago. A subspecies, Belontia signata jonklaasi, is recognised by some authorities for the form found in slower, more turbid lowland waters, distinguished from the nominative form by a turquoise spot at the base of the pectoral fin and a stronger blue wash over the scales in place of the deeper red that characterises clear-water populations.
The species epithet signata is Latin for 'marked' or 'distinguished', likely referring to the characteristic caudal fin extensions. The common name 'combtail' describes the same feature: the elongated, filamentous rays of the caudal fin that fan out to mimic the tines of a comb, particularly well-developed in mature males.
Morphology
Belontia signata is a moderately large labyrinth fish, with FishBase recording a maximum total length of 7 in, though most specimens in both the wild and the aquarium are closer to 4–4.5 in standard length. The body is oval to slightly elongate, laterally compressed, with relatively large scales and a subterminal mouth suited to ambushing invertebrate prey at or near the substrate.
The caudal fin is the defining feature: in adults, particularly males, the central and upper rays elongate into thin, trailing filaments that give the tail a frayed, comb-like silhouette from which both the genus and its common name derive. These extensions continue to develop with age and are more pronounced in mature, well-conditioned males than in females or juveniles. The dorsal and anal fins are also elongated and soft-rayed posteriorly.
Colouration is variable and depends partly on population. The nominative form from clear upland streams is predominantly reddish-brown to brick-red, with an iridescent sheen across the flanks and a series of irregular dark scale markings that produce a reticulated or mottled effect under good lighting. The jonklaasi form replaces much of the red with blue-green and carries a distinctive turquoise or bluish spot at the pectoral fin base. An intermediate form occurs in lowland habitats and lacks the intense red, showing instead a more neutral brownish-olive base with bluish caudal filaments. Sexual dimorphism is moderate: males are somewhat larger, develop longer fin filaments, and typically show brighter colouration; females are slightly smaller with rounder, fuller abdomens.
Habitat
Belontia signata is endemic to Sri Lanka, where it is recorded from several of the island's major river systems on both the wet and dry zones: the Mahaweli, Kelani, Kalu, and Nilwala drainages are confirmed localities. Within these systems it occupies shallow, forested stream environments with relatively clear, slow-moving to gentle-flowing water, typically no more than 3–10 ft deep (averaging shallower in most sampling sites) and often with substrates of sand, small pebbles, or smooth sandstone boulders.
A type-locality stream in the Nilwala basin has been characterised as a low-gradient channel 13–26 ft wide, with sand and silt patches between small smooth boulders and marginal tree roots and overhanging vegetation providing shelter. Water chemistry is mild: pH ranging from approximately 6.0–7.5, temperatures spanning 68–81 °F depending on elevation and season, and hardness between roughly 18–215 ppm across recorded sites — reflecting the diversity of substrate geology across the island's catchments.
As a labyrinth fish, B. signata supplements gill respiration by breathing atmospheric air through the suprabranchial labyrinth organ, an adaptation that allows it to tolerate the occasionally reduced oxygen levels of shaded, slow-flowing forest streams. Adults are described as solitary and territorial rather than schooling; juveniles tend to associate more loosely in small groups.
Feeding
Belontia signata is primarily carnivorous in the wild, with FishBase and field notes indicating a diet centred on terrestrial and aquatic invertebrates — insects, insect larvae, molluscs, and other small invertebrates taken from the substrate and water column. Its relatively large, robust mouth and bold disposition are consistent with an opportunistic predator rather than a grazer or filter feeder.
In the aquarium it readily accepts live and frozen foods such as earthworms, shellfish meat, bloodworm, and brine shrimp; prepared foods including pellets and flake are taken, but live and meaty frozen foods are preferred and improve both condition and colouration. The species is not known to graze significantly on aquatic plants, though it may disturb soft-stemmed vegetation when foraging or rearranging territory.
Mating
Belontia signata is a bubble-nesting species in which the male takes the lead in constructing and defending a spawning site. Unlike the elaborate floating foam rafts built by many gouramis, B. signata constructs a comparatively primitive bubble nest — typically placed under a broad leaf, a submerged rock, or a sheltered crevice near the surface rather than in open water. The male defends the nest site against rivals and intruders with considerable aggression.
Courting males display intensely to females, spreading fins and intensifying colouration. The species is biparental in the sense that both the male and female participate in the spawning and early brood care — an unusual arrangement in bubble-nesting gouramis, where paternal care alone is the norm. Females have been observed tending eggs directly at the nest while males guard the surrounding territory. Given the species' territorial nature, contact between the sexes can be rough outside of spawning readiness, and conditioning and introduction need to be managed carefully in the aquarium.
Breeding
Spawning in Belontia signata follows the bubble-nest template: eggs are laid in or under the primitive mucus-bound nest constructed by the male, typically beneath a floating or submerged leaf. FishBase records clutch sizes of approximately 500 eggs — relatively high for a labyrinth fish of this size. Eggs are described as demersal (sinking), light pink in colour, and small (under 0.5 in). They hatch within approximately 2–3 days at typical tropical temperatures.
Both parents guard the nest and brood during incubation, a biparental arrangement that sets B. signata apart from many bubble-nesting relatives where the male alone tends eggs. The male patrols the perimeter while the female tends the nest more directly. Once the fry become free-swimming, parental behaviour fades and the young should be separated to avoid predation. Fry are raised on infusoria and fine powdered foods initially, graduating to newly hatched brine shrimp as they grow. The three phenotypic forms (nominative, jonklaasi, and the intermediate lowland form) appear to intergrade where their ranges overlap, and separating them in captivity over multiple generations is difficult without documented provenance.
In the aquarium
Belontia signata is not a community fish and should not be treated as one. Adults are territorially aggressive toward conspecifics and toward smaller tankmates, which they may harass or consume outright. A pair or a single specimen in a species tank is the standard approach; if a pair is kept, the tank should be large enough — at least 47 in in length — to allow the female to escape male aggression outside of spawning periods. Hiding places among roots, rocks, and sturdy broad-leaved plants are essential.
Water conditions should mirror the species' Sri Lankan stream origins: temperatures of 75–81 °F, pH around 6.0–7.5, and moderate hardness. Filtration should produce gentle current rather than a strong flow. Surface access is important: as a labyrinth fish, B. signata breathes atmospheric air and must be able to reach the surface freely; a tight-fitting lid also prevents jumping, which the species is capable of. The labyrinth organ requires warm, humid air above the water surface, so the gap between the water and the hood should not be chilled by drafts.
Despite its aggression, B. signata is a long-lived and rewarding species for an experienced keeper who can meet its space and dietary needs. The comb-like caudal filaments of mature males, the rich colouration of clear-water nominative-form individuals, and the unusual biparental care behaviour make it one of the more distinctive gouramis available to the hobby. It is occasionally seen in specialist fish shops and at anabantoid society events, though it is far less common than the more placid gourami species that dominate the trade.
Conservation
Belontia signata is assessed as Vulnerable (VU) on the IUCN Red List, with the most recent assessment dated 5 August 2019 and evaluated against criteria B1ab(iii)+2ab(iii). The listing reflects ongoing decline in the extent and quality of its habitat across Sri Lanka's river systems: deforestation of riparian zones, agricultural encroachment, urbanisation, and associated water-quality degradation have reduced and fragmented the clear, shaded stream habitat the species depends on.
The species is endemic to Sri Lanka with no populations outside the island, making its entire global range coextensive with a single country's freshwater catchments. While it occurs across several major drainages (Mahaweli, Kelani, Kalu, Nilwala), the ongoing contraction of suitable habitat in all of these basins is the basis for the criterion B scoring. Collection for the ornamental trade is a secondary pressure but has historically occurred, given the species' attractive appearance and availability in certain local markets. Captive-bred stock, where obtainable, is preferable to wild-caught; its relative scarcity in mainstream hobby channels means that dedicated enthusiasts and anabantoid societies play an outsized role in maintaining breeding populations outside the wild.