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Betta raja TAN & NG, 2005


Order: Perciformes Family: Osphronemidae


Endemic to parts of the island of Sumatra, Indonesia. The type specimens were collected from a stream named Ayer Merah which is a tributary of the Danau Souak Padang, Jambi province, and it’s found throughout the lowland swamp forest formed by the Batang Hari River in Jambi.

B. raja has also been collected from various localities in Riau province (river Indragiri basin), northern Sumatra Selatan province and Sumatra Barat province, in the eastern regency of Sawahlunto Sijunjung. Populations from the different localities should ideally be labelled as such by collectors/enthusiasts in order to maintain accuracy and preserve pure bloodlines.


Found in lowland forest swamps containing both clear and black water. Presumably it prefers the type of habitat favoured by most other Betta species ie. shaded, quiet waters where overhanging/marginal vegetation grows thickly or among leaf litter and submerged roots.

In a black water lake draining into the Batang Hari river B. raja was recorded alongside numerous other species including Osteochilus spilurus, Parachela oxygastroides, ‘Puntius johorensis, Rasbora cephalotaenia, Mystus bimaculatus, Pseudomystus leiacanthus, Kryptopterus macrocephalus, Silurichthys indragirensis, Pseudeutropeus brachypopterus, P. moolenburghae, Chaca bankanensis, Nandus nebulosus, Helostoma temminkii, Belontia hasselti, Betta coccina, Betta renata, Luciocephalus pulcher, Parosphromenus sumatranus, Sphaerichthys osphromenoides, Trichopodus leeriiChanna lucius and C. striata.

Maximum Standard Length

60 – 70 mm.

Aquarium SizeTop ↑

An  aquarium with base measurements of 80 ∗ 30 cm or equivalent is large enough for a pair or small group.


Can be maintained in a fully-decorated aquarium although many breeders prefer not to use a substrate for ease of maintenance. Driftwood roots and branches can be used and placed such a way that a few shady spots are formed.

If you can’t find driftwood of the desired shape common beech or oak is safe to use if thoroughly dried and stripped of bark. Clay plant pots or lengths of piping can also be included to provide further shelter.

The addition of dried leaf litter, with beech, oak or Ketapang almond leaves all suitable, can further emphasise 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.

Like others in the genus this species seems to do best under fairly dim lighting. You could add aquatic plant species that can survive under such conditions such as Microsorum pteropusTaxiphyllum barbieri or perhaps some potted Cryptocoryne spp., and a few patches of floating vegetation would be useful to diffuse the light entering the tank.

Filtration need 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 – 27 °C

pH: Values over the range 4.0 – 7.0 have been recorded in its natural waters.

Hardness0 – 179 ppm. Captive-bred fish have spawned in water with a value of 20°dH.


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.

It can be maintained in a pair or group and will display some interesting behavioural interactions under the latter circumstances.

Sexual Dimorphism

Males grow larger, possess a greater amount of iridescent scaling on the head, a broader head shape, and more extended fins than females.


Paternal mouthbrooder. Ideally 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.

Following a protracted courtship, eggs and milt are released during an ’embrace’ typical of osphronemids in which the male wraps his body around that of the female. Several ‘dummy’ embraces may be required before spawning commences.

Fertilised eggs are caught on the anal fin of the male then picked up in the mouth of the female before being spat out into the water for the male to catch. Once the male has all the eggs in his mouth the cycle is repeated untill the female is spent of eggs, a process which can take some time.

A brooding male may swallow or release the eggs prematurely if stressed or inexperienced, so it’s preferable to leave the female and any other fishes in situ. The incubation period is 9-16 days at the end of which the male will begin to release fully-formed, free-swimming fry. At this point they can be removed or left to grow alongside the parents, though some may be lost to predation under the latter circumstances.

The fry are large enough to accept motile foods such as 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.

NotesTop ↑

Prior to description this species was widely misidentified as Betta fusca. It’s  included in the B. pugnax complex of closely-related species within the genus, an assemblage of which members share the following set of characters: relatively large head measuring 28-40% SL; live colouration usually brown with green or blue iridescent spots; male with similarly-coloured scales on opercle, sometimes extending to abdomen; juveniles and females usually brown with two central body stripes and a dark marking on the caudal peduncle; anal-fin in mature specimens pointed and often elongated; caudal-fin lanceolate.

It should be noted that not all authors consider the B. pugnax group to contain the same species, with some placed in the B. picta complex by Schindler and Schmidt (2006), for example.

B. raja can be told apart from other members of the B. pugnax group by the following characters: mature males with very long pelvic fins covering 15-23 anal-fin rays or even longer than the base of the anal-fin in some cases; anal-fin and lower caudal-fin with black marginal bands; 25-28 anal-fin rays; 30-32 lateral scales; head length 33.9-37.4 % SL; predorsal length 20.0-24.6 % SL; preanal length 46.1-52.4 % SL; length of body 62.8-70.7 % SL.

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. Tan, H. H. and P. K. L. Ng, 2005 - Raffles Bulletin of Zoology Supplement (13): 115-138
    The labyrinth fishes (Teleostei: Anabantoidei, Channoidei) of Sumatra, Indonesia.
  2. Schindler, I. and J. Schmidt, 2006 - Zeitschrift für Fischkunde 8(1/2): 47-69
    Review of the mouthbrooding Betta (Teleostei, Osphronemidae) from Thailand, with descriptions of two new species.
  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.
  4. 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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