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Betta splendens REGAN, 1910

Siamese Fighting Fish


Order: Perciformes Family: Osphronemidae


Described from the ‘Menam’, a former name for the Chao Phraya river, central Thailand. The precise type locality is unknown, but the species is widespread in the Chao Phraya watershed.

It thus occurs throughout central Thailand, from Chiang Rai province in the north to the Isthmus of Kra at the top of the Malay Peninsula. It’s replaced by B. smaragdina in eastern Thailand and B. imbellis in southern (peninsular) Thailand.

Introduction of ornamental forms and other Betta spp. is known to be having an adverse effect on the purity of some wild populations, the species having been heavily line-bred for aggression in central Thailand, where it’s used in organised fighting matches, and for the aquarium hobby, with many different strains available. It’s also been introduced elsewhere, with feral populations now established in several other countries.


Inhabits still and sluggish waters, including rice paddies, swamps, roadside ditches, streams and ponds. These are often shaded by submerged, surface or marginal vegetation and sometimes contain little dissolved oxygen. Water conditions tend to vary and change rapidly during the annual monsoon season. Substrates can vary from leaf litter to mud, sand, or deep sediment.

Habitat loss or modification across its natural range has increased significantly in recent years and is exerting a significant detrimental effect on wild populations. While most populations inhabit freshwaters some are found in brackish coastal swamps.

Maximum Standard Length

60 – 70 mm.

Aquarium SizeTop ↑

An  aquarium with base measurements of 45 ∗ 30 cm or equivalent is large enough for a single male or pair. SF does not support the practice of keeping this species in tiny aquaria or small jars .


This species does best in a well-planted, shady tank with plenty of surface cover in the form of tall stem plants, floating types such as Salvinia or Riccia spp. or tropical lilies from the genus Nymphaea. Cryptocoryne spp. are also a good choice and will cope with the dim conditions.

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 – 30 °C

pH: Wild-collected fish are likely to prefer a value between 5.0 – 7.0, but the ornamental strains are unfussy with a range of 6.0 – 8.0 acceptable.

Hardness0 – 357 ppm; see comments under pH on wild vs. captive-bred fish.


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.

Avoid keeping it with anything similarly-shaped or with trailing finnage as a male may see these as rivals. Males from the aquarium trade seem more aggressive than any other Betta species, including others from the B. splendens group, and only a single individual can be kept per tank in most cases. A popular option is to keep a single male alongside several females.

Sexual Dimorphism

Males are more colourful and develop more-extended fins than females, this being taken to extremes in many ornamental strains (see ‘notes’).


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 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 been hybridised with domesticated B. splendensB. imblellis and the undescribed B. sp. ‘Mahachai’ and selectively line-bred for the aquarium trade, leading to the development of a number of colour forms that do not occur naturally.

NotesTop ↑

This species lends its name to 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.

The unique combination of characters distinguishing B. splendens from others in the group is as follows: no iridescent scales on opercle; opercle with red-coloured parallel vertical bars; fins in male blue, green, or red; head and body relatively stocky with depth 27.1-32.2 % SL.

The common name is derived from the tradition of keeping the fish in order to fight against each other in organised ’bouts’ upon which participants and onlookers place wagers.

It’s line-bred for vigour and strength which has resulted in hybridisation with B. imbellis and B. smaragdina as well as introduction of line-bred fish to wild populations in order to maintain genetic diversity, a practice which has now made it tricky to locate pure wild populations. The vernacular name ‘plakat’, often applied to short-finned ornamental strains, is derived from ‘pla kat’, the local vernacular name for all members of  the B. splendens group.

The wild form is rarely seen in the aquarium hobby but there exist countless ornamental strains which vary tremendously in colour pattern, finnage, quality and price. The cheap, ‘veiltail’ strains found on sale in the majority of shops are mostly mass-produced in Southeast Asia or Eastern Europe and often exhibit genetic defects or other health issues, so we recommend finding a reputable private breeder if possible.

Females are also available in a myriad of colours, and some commercial breeders have apparently taken to producing very short-finned males which are subsequently sold as females, purportedly in order to discourage private breeding efforts.

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. Regan, C. T., 1910 - Proceedings of the Zoological Society of London 1909(4): 767-787
    The Asiatic fishes of the family Anabantidae.
  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. 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.
  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.

One Response to “Betta splendens – Siamese Fighting Fish”

  • LyraGuppi

    “A popular option is to keep a single male alongside several females.”

    Excuse me if I’m wrong, but I’ve read and heard that males and females should not be kept together unless they are spawning.
    (Unless, you guys mean a extremely large and planted aquarium, but that is still very risky?)

    Was this referring to a sorority, were only females are kept together?

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