Taxonomy & naming
Betta andrei was formally described by Heok Hee Tan in 2023 in the Raffles Bulletin of Zoology, based on a holotype (ZRC 64279, 2 in SL) collected from Singkep Island in the Lingga Archipelago, Riau Province, Indonesia. Eschmeyer's Catalog of Fishes (California Academy of Sciences) lists the valid name as Betta andrei Tan, 2023, placed in the family Osphronemidae.
The species belongs to the waseri species group — a clade of larger, paternal mouthbrooding Betta characterised by blackwater habits, relatively elongated bodies, and elaborate throat markings. The waseri group was circumscribed and reviewed by Ng and Kottelat (1994), who established the broad grouping within which B. andrei nests. Its closest described relative is Betta spilotogena, another Lingga Archipelago endemic, from which B. andrei is separated by the diagnostic pitcher-shaped black patch on the throat rather than the spotted or blotched pattern seen in spilotogena.
Morphology
The holotype measures 2 in standard length (SL), and the species falls toward the smaller end of the waseri group, members of which span roughly 2.5–3.5 in SL as adults. The body is described in the original description as relatively long and stout, consistent with the broader group habitus. Coloration in life features golden iridescent scales on the flanks, set against a brown to dark body ground colour typical of peat-swamp Betta.
The single most diagnostic character is a large black pitcher-shaped mark on the throat — a bold, well-defined patch that separates B. andrei from every other member of the waseri group. Males typically show more intense iridescence than females, and the throat marking may be more vivid or differently developed between sexes, though full sexual dichromatism data await further study of living specimens.
Habitat
Betta andrei is known from Singkep Island, part of the Lingga Archipelago in the Riau Islands province of Indonesia — a region of Sundaland lowlands where peat swamp forest once covered much of the landscape. Its habitat is the acid blackwater streams and peat swamp pools characteristic of intact swamp forest: water stained dark with tannins and humic acids, soft, with very low mineral content, and with pH measured at 3.4–5.5 in comparable waseri-group sites across Borneo and Sumatra.
The water is still to very gently flowing, shaded by dense forest canopy, with abundant leaf litter on the substrate and submerged root systems providing cover. Temperatures in lowland Sundaland peat swamps run warm year-round, typically 75–86 °F (75–86 °F). Like all labyrinth fishes (family Osphronemidae), B. andrei breathes atmospheric air through a suprabranchial labyrinth organ, an adaptation that permits survival in the oxygen-poor, stagnant water of peat swamps where dissolved oxygen can be close to zero.
Feeding
No formal dietary study has been published for Betta andrei. In the wild, waseri-group Betta are presumed to be carnivores that take small invertebrates available in peat-swamp habitats: aquatic insect larvae, small crustaceans, worms, and terrestrial insects that fall onto the water surface. The low-productivity, acid nature of peat swamp systems means prey density is relatively low and feeding is likely opportunistic.
In aquarium settings, waseri-group Betta are typically fed live and frozen invertebrates — bloodworm, Daphnia, Artemia, and similar small prey — to replicate natural foraging and maintain condition. As with all paternal mouthbrooders, it is important to note that brooding males fast entirely throughout the incubation period (roughly one to two and a half weeks), so feeding strategy must account for the male's extended periods without food.
Mating
Betta andrei is a paternal mouthbrooder, as is characteristic of the entire waseri group. Courtship follows the typical Betta pattern: the male displays to the female using fin flaring, body undulation, and lateral posturing, with his intensified colouration and iridescence serving as honest signals of fitness. The female, once receptive, approaches and the pair engage in a spawning embrace.
During the embrace, the male wraps his body around the female in the nuptial clasp common to Betta, and the female releases a small batch of eggs that are fertilised by the male. After each embrace the male immediately gathers the fertilised eggs from the water — either directly or after the female assists in collecting them — and takes them into his buccal (mouth) cavity. The pair typically embrace multiple times until the female is spent, after which the female retreats and the male begins his incubation fast.
Breeding
Once eggs are secured in the male's buccal cavity, he fasts entirely, neither eating nor releasing the clutch until the fry are free-swimming and sufficiently developed. Incubation within the buccal cavity lasts roughly one to two and a half weeks depending on temperature and clutch size — the warmth of the water and the number of eggs both affect development rate. During this period the male should not be disturbed or stressed, as a stressed mouthbrooder may swallow or prematurely release the brood.
Fry emerge from the male's mouth as miniature versions of the adult, already capable of independent swimming. Breeding accounts for this species specifically are sparse, but parallels with other waseri-group members indicate that extremely acidic water is required for successful spawning: optimal breeding pH has been reported at approximately 3.8, consistent with the species' peat-swamp origin. Attempting to breed B. andrei at neutral pH is likely to result in failed embraces or infertile eggs. Breeders maintaining this species typically work with reverse-osmosis water acidified with peat extract or blackwater conditioners to reach the target chemistry.
In the aquarium
Betta andrei is a specialist fish suitable for experienced aquarists who can reliably maintain extreme blackwater conditions. The non-negotiable requirement is soft, very acidic water: pH in the range of approximately 3.5–5.0, very low hardness, and generous tannin input from peat, dried leaves (Indian almond, oak), or blackwater extract. Standard tap water, even if dechlorinated, will be too alkaline and mineral-rich; reverse osmosis or deionised water, acidified with organic materials, is the typical base.
Temperature should be maintained in the warm tropical range (77–84 °F / 77–84 °F). As a labyrinth fish, B. andrei must have unobstructed access to the water surface to breathe atmospheric air; a tight-fitting lid that retains warmth and humidity directly above the waterline is essential, particularly in cooler climates where a cold air pocket above the surface can injure the suprabranchial organ. Filtration should be very gentle — a small sponge filter is appropriate — since the fish is adapted to near-still water and strong flow is stressful.
The species is best maintained as a species-only pair or small group in a heavily planted, dimly lit tank with abundant leaf litter and driftwood. Its quiet demeanour and modest size make it undemanding in terms of space, but the extreme water chemistry requirements and the care needed during mouthbrooding make it a fish for dedicated specialists rather than community aquarists.
Conservation
Betta andrei has not been assessed by the IUCN Red List; its status is Not Evaluated (NE). The species was only formally described in 2023 and as yet there are no published population estimates, no formal range surveys, and no quantitative assessment of threats.
Nonetheless, the biological context is concerning. Singkep Island's peat swamp forests have faced the same pressures as peat swamps across the Riau Islands and wider Sundaland: drainage for agriculture (particularly oil palm and acacia pulp plantations), peat fires associated with land-clearing, and unsustainable logging have reduced peat swamp extent dramatically across the region. A species confined to a single island, restricted to intact peat swamp habitat, and embedded in a habitat type under severe regional decline is inherently at risk even before any population-level data are gathered. Betta andrei should be a priority for formal assessment, and any aquarium interest in the species should be met with captive-bred stock to avoid adding wild-collection pressure to an already threatened endemic.