Taxonomy & naming
Betta tomi 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 (volume 42). The holotype is ZRC 35409, a male of 3 in standard length collected from a tributary of Sungai Mupor approximately 9 mi from Kota Tinggi toward Mersing, eastern Johor, at roughly 103°56′E. Eschmeyer's Catalog of Fishes treats the name as valid and unrevised.
The waseri group currently comprises four species of large, mouthbrooding wild betta found across the southern part of the Malay Peninsula and on the larger Sundaic islands. Within the group, B. tomi is distinguished by the combination of two black oval spots on the throat that do not merge with the lower lip, and the shortest subdorsal scale count of the four species (5–5.5 rows, mode 5). The specific epithet has not been publicly explained by the authors in available literature; no widespread vernacular name is established in the English-speaking aquarium hobby.
Morphology
Betta tomi is a large species for the genus, reaching 2.5–3.5 in standard length. Like other waseri-group bettas it is elongate and laterally compressed, with the broad, rounded caudal fin and relatively robust build typical of the larger mouthbrooding Betta. The dorsal and anal fins are long-based and somewhat pointed, and the ventral fins are filamentous in males.
The colour pattern is described by Ng and Kottelat as the most intense of the four waseri-group species. Males display iridescent blue-green scales on the body, reddish fins, and the diagnostic paired black oval spots on the throat. Females are more subdued in colouration, lacking the full iridescence of displaying males. The throat spots — present in both sexes but most prominent in males — are a key diagnostic character separating this species from the otherwise similar B. waseri and B. pi.
Habitat
Betta tomi is a specialist of freshwater peat swamp forest — the dark, shallow, still or very slow-flowing streams and pools that form beneath the closed canopy of lowland swamp forest on the eastern Johor coast. The substrate is very soft mud overlain by abundant leaf litter and decomposing organic detritus. Water colour is clear to pale tea-coloured from dissolved tannins and humic acids, and pH is recorded at approximately 5.5 — strongly acidic, very soft, and low in dissolved minerals.
As a labyrinth fish, B. tomi supplements gill respiration by breathing atmospheric air at the surface via its suprabranchial organ, which allows it to survive in the low-oxygen conditions typical of stagnant swamp water. The species was found sympatrically with Betta pugnax and Trichogaster trichopterus at the type locality. The entire known range is restricted to eastern Johor; historical records from a Mandai swamp in Singapore (CAS 133176, seven specimens collected in 1937) are now tentatively referred to this species, but swamp habitat destruction has rendered it extinct in Singapore.
Feeding
No published feeding study specific to Betta tomi exists in the available literature. By analogy with other large, peat-swamp Betta, the diet is almost certainly carnivorous — small aquatic invertebrates, insect larvae, small crustaceans, and terrestrial insects that fall onto the water surface among the leaf litter. The organic-rich, low-light swamp environment supports a diverse benthic invertebrate community, and the species' large mouth and elongate body are consistent with an ambush or slow-stalking predator approach.
In the aquarium, wild-type waseri-group bettas typically accept live and frozen invertebrate foods — bloodworm, Daphnia, brine shrimp, small earthworms — and can sometimes be trained onto high-protein pellets. Gut-loading and varied diet are important for maintaining the species' colour and breeding condition.
Mating
Betta tomi is a paternal mouthbrooder, as are all members of the waseri group. Courtship follows the pattern typical of mouthbrooding Betta: the male displays to the female with spread fins and intensified colour, and the pair engage in repeated nuptial embraces in open water or among vegetation and leaf litter. During each embrace the female releases eggs which are fertilised externally.
After spawning the male collects the fertilised eggs into his buccal cavity. Unlike bubble-nesting bettas, there is no nest construction and no egg-attending phase at the surface; instead the entire incubation burden is taken up immediately by the male. The female plays no further role after the spawning sequence is complete. Males of mouthbrooding Betta fast completely during the incubation period and do not feed until the fry are released.
Breeding
Following fertilisation the male holds the eggs — and subsequently the developing embryos and early fry — in his mouth for approximately one to two and a half weeks, eating nothing throughout. The fry are released as free-swimming juveniles capable of taking small live foods. Brood sizes in waseri-group bettas are relatively modest compared with bubble-nesting species, reflecting the greater investment per offspring inherent in mouthbrooding.
In captivity, breeding B. tomi requires replication of the species' soft, acidic blackwater conditions: very low conductivity, pH in the region of 5.0–6.5, warm temperatures, and the absence of strong water movement. Dense cover of floating plants, dried leaves, and low light encourage natural behaviour. The male should not be disturbed during incubation, and the holding male must not be fed. Separating the female after spawning avoids her harassing the brooding male. The species is rarely kept or bred outside specialist collections, and captive experience with it is limited.
In the aquarium
Betta tomi is a demanding and uncommon species in the aquarium hobby, suited to experienced keepers with a specific interest in wild bettas. Its requirements are exacting: very soft, acidic blackwater with pH around 5.0–6.5 and very low mineral content, warm temperatures in the 75–82 °F range, near-zero surface agitation, and a dark, heavily planted tank with abundant leaf litter. The labyrinth organ requires unobstructed access to the air surface, so the space between water and cover glass must be warm and humid rather than cold and dry.
The species is large and predatory; tankmates, if any, must be chosen with care to avoid fin-nipping or predation on small fish. Its cryptic, slow-moving habits and sensitivity to water quality make it unsuitable for a community aquarium. Being wild-caught or F1 from wild-caught parents in most collections, it may be stressed by handling and transit, and quarantine protocols are important. Given its Endangered status in the wild, any captive breeding effort is of genuine conservation value, and keepers are encouraged to document and share successful spawning data.
Conservation
Betta tomi is listed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), assessed on 5 January 2019 by B. W. Low. The assessment reflects an extremely restricted extent of occurrence centred on the peat swamp forests of eastern Johor, combined with continuing decline in the extent and quality of that habitat. Peat swamp forest across Sundaland — Peninsular Malaysia, Sumatra, and Borneo — has been converted at high rates to oil palm, pulp-wood plantations, and urban development. For a species restricted to a single coastal lowland region, even moderate habitat loss translates directly to population decline.
The Singapore population is already extinct, lost when the Mandai swamp and other lowland habitats on the island were cleared during the twentieth century. The remaining range in eastern Johor is subject to ongoing development pressure. Research published on ResearchGate has documented that peatland conversion in Sundaland carries freshwater fish extinction risk, with Betta tomi among the flagged species. There are no known captive breeding programmes of conservation scale, and the species' rarity in collections means that ex-situ insurance populations are essentially absent. Protection and restoration of peat swamp habitat in Johor, together with formal reserve coverage of the type-locality watershed, represent the most realistic conservation levers available.