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siamorientalis: derived from Siam, the former name of Thailand, and the Latin orientalis, meaning ‘of the east’, in reference to this species’ type locality in eastern Thailand.


Order: Perciformes Family: Osphronemidae


Currently known only from Chachoengsao, Sa Kaeo, Prachin Buri and Chon Buri provinces in eastern Thailand plus Banteay Meanchey province in western Cambodia (which borders Sa Kaeo) and at least one unspecified locality in Vietnam so it appears to be quite widely-distributed.

Type locality is ‘Sai Hai village (13°42′ N, 101°13′ E), Tha Thonglang subdistrict, Bang Khla district, Chachoengsao province, Thailand’.


This species occurs in still or slowly-moving water where it takes shelter and builds its bubble nests (see ‘Reproduction’) among submerged vegetation.

It’s been collected from shallow freshwater marshes, flooded fields and rice paddies plus heavily-vegetated marginal zones of ponds, lagoons, ditches, canals and others water bodies.

The commonest aquatic plants encountered in these habitats during field work were Leersia hexandra (Poaceae) and Eleocharis dulcis (family Cyperaceae).

Sympatric fish species included Trichopsis vittata, Trichopsis shalleri, Trichopsis pumila, Trichopodus trichopterus, Anabas testudineus, Lepidocephalichthys hasselti, Pangio anguillaris, Macrognathus siamensis and Monopterus albus.

Maximum Standard Length

25 – 33 mm.

Aquarium SizeTop ↑

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


Should fare best in a well-planted, shady tank with plenty of surface cover in the form of tall stem or floating plants.

Driftwood roots and branches can be used and placed such a way that a few shady spots are formed while clay plant pots or lengths of piping can also be included to provide further shelter.

The addition of dried leaf litter further emphasises the natural feel and as well as offering additional cover for the fish brings with it the growth of microbe colonies as decomposition occurs.

These can provide a valuable secondary food source for fry and the tannins and other chemicals released by the decaying leaves are also considered beneficial for fishes from blackwater environments.

There is no need to use natural peat, however, the collection of which is both unsustainable and environmentally-destructive.

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

pH5.5 – 7.5

Hardness18 – 215 ppm


Likely to feed mostly on insects and other small invertebrates 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 newly-hatched 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 be sure to research your choices before purchase.

When plenty of cover and broken lines-of-sight is provided it should be possible to keep more than one male per tank although it’s recommended to isolate pairs for breeding purposes.

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.

It 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, 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.

NotesTop ↑

This species was considered a colour form of the closely-related B. imbellis and commonly-referred to as ‘black imbellis’ prior to description due to its blackish opercle and body.

It’s also previously been confused with B. splendens due to the colour of the vertical opercular bars which tend to be reddish (but may also be pale red, greenish-silvery, plain silvery or without colour in some populations), but DNA analysis has demonstrated it to be a distinct species (Kowasupat et al., 2012).

B. siamorientalis is included in the Betta splendens group 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.

It can be distinguished from other members of the B. splendens group by the following combination of characters: body dark-brown to black; opercle black with two parallel, reddish vertical bars; operculum membrane dark-brown to black with red patches; caudal-fin rays with a red, crescent-shaped distal band and thin black edge; caudal-fin without dark transverse bars; distal half of posterior anal-fin rays red with a small red patch at the distal tip; pelvic-fin black and red with a white tip.

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.

Betta 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 putative groups containing closely-related species is now generally accepted but largely based on morphological and behavioural characters meaning molecular phylogenetic work may 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 T. Jeenthong, 2012 - Vertebrate Zoology 62(3): 387-397
    Betta siamorientalis, a new species of bubble-nest building fighting fish (Teleostei: Osphronemidae) from eastern Thailand.
  2. 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.
  3. Witte, K.-E. and J. Schmidt, 1992 - Ichthyological Exploration of Freshwaters 2(4): 305-330
    Betta brownorum, a new species of anabantoids (Teleostei: Belontiidae) from northwestern Borneo, with a key to the genus.

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