Taxonomy & naming
Betta mulyadii was described by Ding, Lei, Haryono, Shi & Zhang in 2025, based on specimens collected from a single peat-swamp site in the Duri area of Riau, Sumatra Island, Indonesia. The description was published in ZooKeys (doi: 10.3897/zookeys.1238.142857). The holotype is a male, 0.5 in SL, catalogued as MZB.26964; paratypes (NCUMB.65326) range from 1 in SL.
The species belongs to the coccina group — a cluster of small, red-hued Betta from the peat-swamp and blackwater forests of Sundaland. Within this group it is distinguished from close relatives by the absence of a green iridescent mid-lateral patch on the body and by the combination of meristic characters: 8–10 dorsal-fin rays and 5–6 subdorsal scales. The valid name as governed by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is Betta mulyadii Ding, Lei, Haryono, Shi & Zhang, 2025.
The species was first encountered in 2012 by Mulyadi Tjoa Hong Tjai, whose name the epithet honours. The common name api-api is Bahasa Indonesia for flame or fire — a fitting reference to the reddish colouration.
Morphology
Betta mulyadii is a small fish even by coccina-group standards, with standard length running from 0.5 in (holotype male) to a maximum of 1 in SL recorded among paratypes; FishBase records a maximum of 1 in SL. The body is slender and elongate in the typical wild-betta manner, laterally compressed, with the rounded head and upturned mouth characteristic of labyrinth fishes.
The overall coloration is red throughout the body — a feature that ties it to the other fire-coloured members of the coccina group. The distinguishing mark is the absence of a green iridescent patch on the mid-lateral flank that is present in several related species. The unpaired fins (dorsal, caudal, and anal) are red with bright bluish margins, giving the fish a two-tone fin edge under good light. Males are presumed to show more intense colouration than females, as is typical in the group, though detailed sexual dichromatism data are sparse for this newly described species.
Habitat
The entire known range of Betta mulyadii consists of a single small forest peat swamp in the Duri area of Riau province, Sumatra, with an area of occupancy estimated at less than 3 mi². The swamp sits within an oil-palm agricultural landscape and is adjacent to active oil wells — two of the primary industries that have transformed lowland Riau over recent decades.
As a member of the coccina group and a Sumatran peat-swamp endemic, B. mulyadii inhabits water that is characteristically warm, extremely soft, highly acidic, and tea-coloured from dissolved humic and tannic acids leaching out of the surrounding peat. Oxygen concentrations in such waters can be very low, particularly near the substrate and in stagnant pools — the ecological pressure that drove the evolution of the labyrinthine suprabranchial organ shared by all Betta. Access to the water surface for aerial respiration is therefore as important as dissolved oxygen in the water column itself.
Syntopic species recorded at the site include Betta cf. pugnax and the rasbora Rasbora einthovenii, both consistent with a Sundaland peat-swamp community.
Feeding
No specific dietary studies are available for Betta mulyadii. Like other members of the coccina group and wild bettas generally, it is almost certainly a micro-predator, feeding on small invertebrates within or at the surface of the water column: chironomid larvae, small crustaceans, and surface-fallen invertebrates would form the bulk of a natural diet in a peat-swamp setting.
In captivity, coccina-group bettas typically accept live and frozen small invertebrates — Daphnia, micro-worms, newly hatched brine shrimp, small bloodworm — but can be difficult to wean onto prepared foods. Given the species' small adult size and the fragile nature of its wild population, the number of B. mulyadii in captivity is negligible and no established husbandry record for this species' diet exists as of the date of description.
Mating
Betta mulyadii is a bubble-nesting species, as expected for all members of the coccina group. In bubble-nesting bettas, the male constructs a raft of mucus-bound air bubbles at the water surface, typically anchored beneath a floating leaf or piece of emergent vegetation. The nest serves as the site for courtship, spawning, and early larval development.
Courtship follows the pattern common to the genus: the male displays with flared opercula and extended fins, intensifying his colouration to signal fitness to the female and to dissuade rival males. The female signals receptivity by adopting a submissive posture or approaching the nest area. Spawning occurs in a nuptial embrace beneath the bubble raft, the male wrapping around the female as eggs are released and fertilised.
Breeding
Following the spawning embrace, the male gathers the fertilised eggs and deposits them into the bubble nest, where buoyancy and the mucus coating protect them. He then takes sole charge of nest maintenance and guarding, repairing broken bubbles and retrieving fallen eggs or early larvae. The female typically plays no further role and may be driven off or even threatened by the guarding male.
Specific incubation times and fry-rearing data for B. mulyadii are not yet documented in the literature given its only-recent formal description and the negligible number of specimens in captive collections. By analogy with other coccina-group bubble-nesters kept in soft, warm, acidic water (pH 4–5.5, temperatures 79–82 °F), eggs would be expected to hatch within 24–48 hours and the larvae to become free-swimming within two to four days of hatching, at which point they require very small first foods such as infusoria or freshly hatched nauplii.
In the aquarium
Betta mulyadii is not established in the ornamental-fish hobby and is unlikely to be encountered in trade in the foreseeable future. Its extreme rarity in the wild, combined with its very recent formal description (2025), means that captive stock is essentially non-existent outside of any specimens held by the researchers involved in the original description.
Were the species to become available through responsible captive-breeding programmes, husbandry would follow the template for other coccina-group bettas: a small, well-planted species tank or heavily shaded biotope setup with blackwater chemistry (very soft, pH 4.5–5.5, temperatures 79–82 °F), gentle or minimal filtration, a tight-fitting lid (labyrinths must access warm, humid air above the surface), and live or frozen small invertebrates as the dietary staple. Because coccina-group males are intolerant of one another, only one male should be kept per enclosure. The species' conservation status makes any acquisition from wild sources indefensible; only captive-bred individuals should be considered.
Conservation
Betta mulyadii is assessed as Critically Endangered under IUCN Criteria B2ab(iii), reflecting an area of occupancy estimated at less than 3 mi², the existence of a single known location, and ongoing decline in the quality and extent of its forest peat-swamp habitat. The assessment was made in the context of the original description (Ding et al. 2025) and had not been formally published on the IUCN Red List website as of the cache date for this article.
The threats driving its decline are among the most powerful forces reshaping Sumatran lowlands: oil-palm agriculture has converted the majority of Riau's peat-swamp forests over the past three decades, and petroleum extraction — with associated drainage, compaction, and contamination — affects the precise area where B. mulyadii was found. The combination of a sub-3 mi² range, a single known site, and two converging industrial pressures places the species at imminent risk of total habitat loss.
No formal conservation measures are known to be in place for this species as of its description. Its survival is contingent on the protection of the residual swamp fragment in the Duri area — a pocket of habitat that currently exists between oil wells and oil-palm rows. Documentation of the species through the original description is a first step, but habitat protection and captive-insurance populations are the interventions that would meaningfully change its outlook.