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Order: Perciformes Family: Osphronemidae


Known only from a handful of localities in Bangkok, Samut Sakhon, Samut Songkhram and Samut Prakan provinces in central Thailand, all of which lie on the coast of the Gulf of Thailand.

Most habitats are in close proximity to Bangkok, which continues to expand rapidly, are considered under extreme threat, and recent surveys have failed to confirm that the fish is still present in Samut Songkhram and Samut Prakan.

Populations from different localities exhibit slight morphological differences, e.g., the shape of the caudal-fin can vary from rounded to ovate, and should not be mixed or hybridised in aquaria.


Inhabits brackish, frequently tidal, coastal swamps and is often associated with the mangrove palm Nypa fruticans, commonly-known as the nipa palm, the only species of palm specifically adapted to estuarine environments.

Males build their bubble nests between the palm branches or within the bracts at the base of the trees, these providing protection and shelter. Although brackish populations of both B. imbellis and B. splendens have been discovered t’s the only member of the genus to occur exclusively under such conditions.

PH at habitats in Samut Sakhon province varied between 6.87-7.80 with salinity ranging from 1.1-10.6 ppt. Sympatric fish species include Trichopsis vittata, Trichopodus trichopterus, Anabas testudineus, Aplocheilus panchax, Oryzias javanicus, Dermogenys siamensis, Channa striata, and Boraras uropthalmoides.

Maximum Standard Length

50 – 60 mm.

Aquarium SizeTop ↑

An  aquarium with base measurements of 45 ∗ 30 cm or equivalent is large enough for a single pair.


Can be maintained in medium-hard to hard fresh or slightly brackish conditions, and does best in a well-planted, shady tank with plenty of surface cover in the form of tall stem or floating plants.

Driftwood can also be used and other plants such as Microsorum or Taxiphyllum spp. can be attached to it. Small clay plant pots, lengths of plastic piping or empty camera film cases can also be included to provide further shelter.

The addition of some dried leaf litter (beech, oak or Ketapang almond leaves are all suitable) is also recommended. In addition to offering additional shelter for the fish it brings with it the establishment of microbe colonies as decomposition occurs. These microorganisms can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves are also thought beneficial.

As it naturally inhabits sluggish waters filtration should not be too strong, with an air-powered sponge filter set to turn over gently adequate. Keep the tank well-covered and do not fill it to the top as like all Betta spp. it requires occasional access to the layer of humid air that will form above the water surface, and is an excellent jumper.

Water Conditions

Temperature22 – 28 °C

pH7.0 – 8.5

Hardness90 – 357 ppm


Likely to prey on insects and other small invertebrates/zooplankton in nature. Captive fish will normally accept dried products once they’re recognised as edible, but should be offered plenty of small live or frozen foods such as DaphniaArtemia or bloodworm regularly to ensure development of optimal colour and condition.

Small insects such as crickets or Drosophila fruit flies are also suitable to use; it’s best to fill the stomachs of these by feeding them fish flakes or some kind of vegetable matter before offering them to the fish. Take care not to overfeed as Betta spp. seem particularly prone to obesity.

Behaviour and CompatibilityTop ↑

Not recommended for the standard community set-up for reasons already touched upon. It’s requirements and disposition mean it’s best kept alone or with very peaceful species since much bigger or more vigorous fishes are likely to intimidate and outcompete it. Some small cyprinids and loaches that inhabit similar environments in nature are compatible, but the presence of any other fishes can be a distracting influence should a pair decide to spawn.

Provided with sufficient cover and broken lines-of-sight it’s possible to keep more than one male per tank, though it’s best to isolate pairs for breeding purposes in most cases.

Sexual Dimorphism

Males are more colourful and develop more-extended fins than females.


Bubble-nester. Organise a separate tank for breeding purposes unless the fish are already being maintained alone, setting this up as suggested above. The tank should have the tightest-fitting cover you can find (some breeders use clingfilm instead to ensure no gaps) as the fry need access to a layer of warm, humid air without which development of the labyrinth organ can be impaired.

The pair need not be separated prior to spawning. The male may construct the nest in a tube or canister, under a broad plant leaf or among fine-leaved surface vegetation, and will not usually tolerate the female in the vicinity until it’s complete.

Just prior to spawning the body colour of the female pales and dark bars appear on the flanks, with the act itself normally occurring below the nest in an ’embrace’ typical of osphronemids, with the male wrapping himself around the female. At the point of climax milt and a few eggs are released which the female proceeds to catch between pelvic fins and body.

The male then transfers them to his nest while the female recovers any that fell. This cycle is then repeated until the female is spent of eggs, a process that can take some time.

Post-spawning the adults can normally be left in situ although the female is no longer actively involved with the male assuming sole responsibility for guarding and tending the nest. The eggs hatch in 24-48 hours, remaining in the nest for a further 3-4 days until the yolk sac is fully-absorbed, while the male continues to collecting and return any that fall. If threatened the entire nest may be moved elsewhere. Once the fry begin to swim freely the male will lose interest, but the adults do not usually eat their offspring.

The fry will require an infusoriatype food for the first few days, after which they should be large enough to accept  microworm and Artemia nauplii immediately, though it should be noted that there exist reports of young Betta developing health issues if fed excessive amounts of the latter. Offer small amounts of different foods 2 -3 times per day for optimal growth rate, and don’t change too much water at once, with regular, small changes preferable to intermittent larger ones.

This species has probably been hybridised with domesticated B. splendensB. imblellis and B. smaragdina, leading to the development of a number of colour forms that do not occur naturally.

NotesTop ↑

B. mahachaiensis has been considered a hybrid in the past, but molecular and morphological analyses have confirmed it to represent a distinct species. The specific name is derived from the coastal subdistrict of the same name in Samut Sakhon province, just south of Bangkok, where it was first discovered.

It can be distinguished from congeners by the following combination of characters: base body colour brown to black with iridescent green to bluish-green pigmentation; presence of two parallel iridescent green to bluish-green vertical bars on opercle; brown-to-black opercular membrane without red streaks or patches; dorsal, caudal, and anal-fin rays brown to black contrasting with iridescent green or bluish-green interradial membranes; dorsal fin with transverse black bars in proximal two-thirds or more; absence of dark transverse bars on caudal-fin but presence of small black rounded marks flanking the internal rays on interradial membranes; pelvic fin brown to black with iridescent green/bluish-green anterior margin and white tip; head length 24.9–31.2% SL; postdorsal length 17.1–25.2% SL; length of dorsal fin base 12.2–19.3% SL; pelvic fin length 21.2–49.6%; pectoral fin length 15.4–21.3% SL; orbit diameter 22.8–29.7% SL.

It’s included in the Betta splendens complex of closely-related species within the genus, of which members share the following set of characters: head length short 22-31 % SL; often a brightly-coloured body; iris of the eye with iridescent green or blue patches; body elongate or slender; opercles parallel when head viewed dorsally; caudal-fin rays red or brown and contrasting with the iridescent interradial membranes; unpaired fins without an iridescent margin; opercle with red or blue vertical bars in males; dorsal-fin rays 0-II, 7-9; anal-fin rays II-V, 21-26.

Within the group it can be told apart from described members by the following combination of characters: presence of vertical, parallel blue bars on opercle; 1st pelvic-fin ray blue in colour; caudal-fin green without red, crescent-shaped distal band; body relatively slender.

The genus Betta is the most speciose within the family Osphronemidae with almost 70 recognised members and looks set to grow further with new ones continuing to be described on a regular basis since the turn of the century.

Member species have successfully adapted to inhabit a variety of ecological niches from stagnant ditches to flowing hill streams including some extreme environments such as highly acidic peat swamp forests.

The referral of members to a number of groups containing closely-related species is now generally accepted but largely based on morphological/behavioural characters. Molecular phylogenetic work is thus required and would undoubtedly prove useful in more precisely determining relationships between these fishes.

A full list of the species groups as currently recognised can be found here.

Like others in the suborder Anabantoidei this species possesses an accessory breathing organ known as the labyrinth. So-called due to its maze-like structure this organ allows the fish to breathe atmospheric air to a certain extent.

Comprising paired suprabranchial organs formed via expansion of the epibranchial (upper) section of the first gill arch and housed in a chamber above the gills, it contains many highly-vascularised, folded flaps of skin which function as a large respiratory surface. Its structure varies in complexity between species, tending to be better-developed in those inhabiting harsher environments.


  1. Kowasupat, C., B. Panijpan, P. Ruenwongsa, and N. Sriwattanarothai, 2012 - Zootaxa 3522: 49-60
    Betta mahachaiensis, a new species of bubble-nesting fighting fish (Teleostei: Osphronemidae) from Samut Sakhon Province, Thailand.
  2. Sriwattanarothai N., D. Steinke, P. Ruenwongsa, R. Hanner and B. Panijpan, 2010 - Journal of Fish Biology 77(2): 414-424
    Molecular and morphological evidence supports the species status of the Mahachai fighter Betta sp. Mahachai and reveals new species of Betta from Thailand.
  3. Tan, H. H. and P. K. L. Ng, 2005 - Raffles Bulletin of Zoology Supplement (13): 43-99
    The fighting fishes (Teleostei: Osphronemidae: Genus Betta) of Singapore, Malaysia and Brunei.

One Response to “Betta mahachaiensis”

  • MarZissimo

    Stefano Valdesalici collected them few years ago (2008) around this coordinates: 13° 33′ N 100° 15′ E (very close to Samut Sakhon, in Thailand)
    Now my question is: is it correct calling these fishes Betta mahachaiensis “Samut Sakhon” or them should be labeled with other location-code?


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