Common name – Spotfin betta, Brunei Beauty, Brunei fish

A splendid species of oral incubator Betta is in danger of extinction due to its habitats. Endemic to Borneo, where it is known only from Brunei Darussalam and the northern tip of the Malaysian state of Sarawak. In Brunei, there are numerous well-known locations along the Mendarem River and in the Labi Rainforest, in Labi’s administrative area, which borders Sarawak to the south.
This species’ narrow natural range has led to it being added to the IUCN Red List of Threatened Species, where it is listed as Vulnerable (D2). Criterion “D2” refers to “acute restriction in its area of ​​occupation” and means that a particular species could become endangered or become extinct in a short time. As a result, the Sultan of Brunei banned the species’ export, which means that most of the fish in the hobby probably come from Sarawak, where the species is not protected by law.
Betta macrostoma is still available, but we have not confirmed whether it is being exported illegally or whether it applies only to wild-caught specimens. Those currently shipped are bred in captivity. It also appears that the area where Sarawak’s habitats are located will be transformed into an oil palm plantation in the future.

The Betta macrostoma species is included in the Betta unimaculata complex of closely allied species within the genus Betta, whose members share the following series of characters:

  • long and slender body with depth 18-25% SL at the height of the dorsal fin
  • large, squat head with 19-24% SL width
  • long jaw and lower lip with distance from the tip of the lower jaw to the posterior end of the jaw 27-54% HL
  • caudal fin of rounded shape, occasionally with elongated median rays
  • short and filamentous pelvic fin
  • relatively pointed dorsal and anal fins

The unique combination of characters that distinguish Betta macrostoma from the other group species is the following:

  • red-colored male body
  • male with a red spot on the operculum and an ocello on the dorsal fin
  • operculum devoid of iridescent scales
  • 9-11 rays of the dorsal fin
  • 25-28 rays of the anal fin
  • 6-8 subdorsal scales

It has been observed that the populations of different localities show differences in coloring and the design of the livery. Therefore in the aquarium, they should be kept separately.

female Betta macrostoma

Betta macrostoma Natural Habitat

Environment: benthopelagic, freshwater; tropical climate. It inhabits surface waters (about 30 cm deep) near stagnant pools along stream beds with clay substrate. It is also found in rapids with clear water; it occupies small pools in the tributaries and quiet areas along the main river bed.
It was collected in shady pools above the rainforest waterfalls in both Brunei and Sarawak. The substrates appear to consist mainly of gravel and rocks of various sizes plus scattered piles of fallen leaves from surrounding plants, although Brunei’s location is described as “clayey.” The water flows relatively fast and is quite clear. However, it appears to be slightly brown in some areas, possibly due to the dissolved humic acids and other chemicals released by the decaying organic material. Fish are found in still water pools, and significant river channels and quiet sections of tributaries, with only one adult or one pair of adults, or several juveniles found in each pool.

The dissolved minerals’ content is almost always negligible, the pH was measured between 4.4-5.7 depending on the habitat, and the only sympatric fish species recorded to date is Rasbora tubbi . In most locations, they are also typical of the red-colored shrimp, Macrobrachium sp., Which can form an important part of their natural diet.

female Betta macrostoma

Differences between Male and female

The livery of the male specimens is very colorful and striking: the body is bright red, with light orange reflections and two brown longitudinal lines, not always visible; the head is dark, almost black, with greenish reflections, especially on the forehead; on the branchial operculum an orange stain is drawn; the dorsal fin, of an orange color and with the distal margin of turquoise color, has on the posterior margin, just above the back, a spot of golden yellow, centrally interrupted by one or 2 small black bars, while the rest of the fin is sprinkled with small spots, always golden yellow; the anal fin, of a reddish color like the body, has the distal margin crossed by a dark, anthracite gray or black border; the caudal fin, of a reddish color like the body and with a turquoise distal margin, it is crossed by some semicircular bands, of black color, alternating with as many of golden yellow; the ventral fins are black, with turquoise tips, while the pectoral fins are semi-transparent with turquoise reflections and some black marbling.
The livery of the female specimens, on the other hand, is not very colorful: a pinkish-gray color and with a washed olive greenback; on the side, it has two longitudinal lines of a brownish color; one of these longitudinal lines passes over the eye while the other just above; at the end of the caudal pedinculum there is a small dark, black or brownish point; the fins are semi-transparent.
The male, extremely territorial and aggressive, creates a small harem of females which he strenuously defends from the other males; the first action of this defense consists in the parade, during which, to appear more prominent and more powerful, the dominant male spreads his fins as much as possible and opens his mouth; then, with jerky movements, he joins his rival, trembling to intimidate him; if still not enough to make the intruder desist the real attack begins; the two contenders take each other by the mouth and begin to shoot.

Aquarium Care

Dimension: Maximum in nature 7 cm, In aquarium 4-6 cm
Lifespan: 8 – 10 years
Tank Size: 20+ gallons (80+ liters)
Diet: Omnivore
Temperament: Peaceful once paired
Temperature: 68 – 77 F (20 – 25 C)
Water values
Temperature: 24 ° – 28 ° C
Hardness: 2 ° – 10 ° dGh
PH: 5-7


Carnivorous, in nature, it feeds on small crustaceans, worms, eggs, and insect larvae; in the aquarium, it is demanding as far as food is concerned: it is better to administer frozen artemias and Chironomus frequently, sometimes it also accepts freeze-dried feed and dry feed in flakes or microgranules.


Brunei fish can be kept in a fully decorated aquarium, although many keepers prefer not to use a substrate to facilitate maintenance. Roots and branches of driftwood can be used and placed in such a way as to form some shaded spots.
If you can’t find woods of the desired shape, common beech or oak is safe to use when wholly dried and stripped of the bark. You can also include terracotta plant pots or lengths of piping to provide additional shelter.
Adding dried leaf litter, with beech, oak, or Ketapang almond leaves all suitable, can further emphasize the natural feel and, in addition to offering additional coverage for the fish, brings with it the growth of microbe colonies when the decomposition. These can provide a valuable secondary food source for the fry, and the tannins and other chemicals released by the decaying leaves are also considered beneficial.
Like others of the genus, this species seems to perform best in relatively low lighting conditions. You could add aquatic plant species that can survive in such conditions as Microsorum Pteropus, Taxiphyllum Barbieri, or perhaps some Cryptocoryne spp. Potted and a few floating vegetation patches would be useful to diffuse the light that enters the tank.
Filtration shouldn’t be too strong, with an air-powered sponge filter set to spin properly gently. Keep the tank well covered and do not fill it to the bottom like all Betta spp. It requires occasional access to the layer of moist air that will form above the water’s surface and is an excellent jumper.


The tank should have the tightest cover you can find (some breeders use clingfilm instead to ensure there are no gaps) as the fry need access to a layer of warm, humid air without which labyrinth organ can be compromised.
While this isn’t always possible, the ideal way to get a compatible pair for breeding purposes is to form from a group naturally. If a male and a female are randomly selected, they do not always coexist peacefully, and the weaker individual can even be killed. Once a pair has formed, they usually don’t show any aggression unless space is limited.
Courtship is usually a long relationship during which the intensely colored male approaches the female with his mouth open and fins erect. The female usually orients her body so that the male faces one of her hips and can gasp and a flare-up in response.
The eggs and milt are released in small batches during an osphronemid “hug” in which the male wraps his body around that of the female, and there may be several “mock” attempts before spawning begins.
Both adults have been observed to collect fertilized eggs, with those collected by the female spat into the male’s mouth. Once the male has all the eggs in his mouth, the cycle is repeated until the female has run out of eggs, a process that can take some time.
After spawning, it is crucial to give the male as much peace and quiet as possible. Males of this species are known to swallow broods of eggs after a few days, and the chances of this happening are increased if the male is unduly disturbed.
For this reason, many breeders leave the female in situ rather than risk upsetting the male by removing her. However, in smaller aquariums, in particular, she may excessively harass the male or eat fry and require removal regardless.
The incubation period appears to vary enormously with reports suggesting a range of 14-35 days, after which the male will begin to release the fully-formed, free-swimming fry. Success in breeding them came when they were removed, left next to the male or both adults.
The fry is large enough (5mm +) to immediately accept mobile foods such as microworm and Artemia nauplii (see notes above on feeding Artemia to young Bettas). Feed him small amounts of different foods several times a day for the best growth rate, but be very careful not to overfeed as juveniles of this species can develop intestinal problems very easily if overfed. Even small daily water changes (5 – 10% of the tank volume) should be introduced to avoid organic waste accumulation.

By fishexp