Betta Macrostoma

Betta Macrostoma: The Treasure of Brunei

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There are many different varieties of betta fish to choose from. And the range of colors and fin shapes you can find is dazzling! Given the right tank conditions and diet, bettas are relatively easy to keep, and you can even have a go at crossbreeding them too, which is a fascinating and fun hobby.

In this article, we introduce you to the rare and beautiful betta macrostoma, an exotic and unusual variety of betta that’s rapidly gaining popularity among hobbyists and breeders alike.

What is a betta macrostoma?

The betta macrostoma originates from the small country of Brunei Darussalam on the island of Borneo, which forms part of Malaysia and Indonesia. The betta macrostoma, which means “big mouth,” is also known as the Brunei Beauty and the Ikan Pelaga Brunei. These beautiful fish are mouthbrooders, having an unusually large jaw and mouth, hence their name. 

The betta macrostoma is a wild strain of betta fish, which, unfortunately, currently finds itself on the IUCN red list of threatened species and is classified as “vulnerable.” For over 50 years, it was widely believed that the species had gone extinct, largely because of the destruction of its habitat and the rapid economic and social development that was experienced in the region where the betta macrostoma traditionally lives.

However, in 1981, the betta macrostoma was re-discovered in one of the many waterfalls of Brunei Darussalam. The discovery led to renewed excitement and interest in the species.

The male betta macrostoma has very vivid coloration. They display brilliant orange-red with highly-contrasting black and white markings during courtship and spawning. In comparison, the female macrostoma is a rather drab, silvery-brown fish that has two very distinct lateral bands. You can often view the female fish’s ovum by shining a light on her.

Check out a video of the betta macrostoma in captivity at this link. You can see how the species got its name!

Protected by royalty!

So, what is to become of the endangered betta macrostoma?

Well, help has arrived in the unexpected form of Hassanal Bolkiah Mu’izzadin Waddualah, the Sultan of Brunei. He has taken a special interest in the betta macrostoma and designated the species as protected in Brunei.

That designation prohibits catching, possessing, or keeping captive any wild betta macrostoma in Brunei. 

However, despite having a royal bodyguard, the betta macrostoma has been taken from its homeland and bred in tanks by hobbyists. Consequently, the species is becoming more available to buy from breeders in Singapore and Thailand. Despite the questionable morality of that, enthusiasts are now able to see more of this endangered fish. The practice has also raised the Brunei Beauty’s profile, and perhaps even protected it from extinction in the future.

However, only experienced fish keepers should attempt to keep and breed betta macrostoma. Most serious conservationists and aquarists agree that care is best left to those with a genuine interest in rehabilitating, studying, and perpetuating the species. 

Keeping captive betta macrostoma

When kept in captivity, betta macrostoma should be housed in pairs in species-specific setups or certain community environments. Pairs or groups of macrostoma tend to do very well when kept together for the long-term. It’s not uncommon for spawning to occur spontaneously. Often, spawning is not discovered until the aquarist discovers fry in the tank during regular tank maintenance.

Tank conditions

Betta macrostoma do best in a large tank of at least 40 gallons. As for the tank setup, the habitat should be well-planted and kept covered to prevent the fish from jumping out. Like all wild bettas, the betta macrostoma is a very adept jumper and will escape through the tiniest hole in a tank hood. So choose a tank that has a close-fitting lid or cover. 

Betta macrostoma have been labeled as difficult fish to keep. Individual fish can survive in a large range of ecological states, as long as the quality of the water is correctly maintained. However, the highest incidences of spontaneous spawning take place in soft water with <6 pH between 700 and 750 Fahrenheit.

What appears to be the most important thing to the betta macrostoma as regards water quality is that conditions remain consistent. These fish do not tolerate unstable or shifting water parameters. 


Betta macrostoma are omnivorous and tend to do well on a varied diet. For example, frozen beef heart, daphnia, bloodworms, brine shrimp, and many varieties of dried commercial foods are all appropriate.

Betta macrostoma spawning

Parent Behavior

Spawning usually lasts for between two to four hours. It follows the pattern of typical betta spawning behavior, with the male embracing the female. 

Both parents gather the eggs as they release, with the female fish passing the eggs that she has collected to the male. It’s not uncommon for the female to hold the eggs in her mouth for quite a length of time before the male is ready to accept them from her. Sometimes, the male will swallow and eat the eggs, but the pair will usually spawn again around two weeks later.

Male macrostoma that are carrying eggs take on a very distinctive “bulldog” look, with their lower jaw protruding and their mouth obviously full. Incubation usually takes around 30 to 35 days, during which time the male fish will not eat at all.

The Fry

The fry hatch from the eggs in batches. Newly hatched fry are around 0.2 to .39 inches long and fully independent. Some breeders recommend that the male betta macrostoma be isolated immediately after spawning and until the fry are released, at which time he is removed. Other experts suggest keeping the breeding pair together throughout the entire holding period, reporting cooperation between both parent fish in the care of the newborn fry.

However, the longer the parents remain with the fry, the higher the likelihood of cannibalism. So, if you want to preserve all or most of the fry, remove the parents after around five to seven days and leave the fry to fend for themselves.

Once the fry emerge, you will need to feed them. Betta macrostoma fry do extremely well on the same first foodstuffs as other species of bettas, such as micro-worms, BBs, vinegar eels, and other small nematodes.

In large, well-planted, well-filtered tanks, it’s not unusual to keep a breeding pair of betta macrostoma together. They spawn naturally and live with their offspring. Provided that the tank has plenty of cover and dense planting, macrostoma fry and juveniles are pretty good at evading pursuit and can be removed from the breeding setup as soon as they are large enough to net.

Juvenile betta macrostoma are usually around two inches in length by the time they reach the age of six months. That is assuming they receive a proper diet and have a well-kept tank. At this time, you should be able to identify males and females, making it fairly straightforward to separate them.

Final thoughts

Few betta enthusiasts would argue that the rare betta macrostoma is a breathtakingly beautiful fish. And now, thanks to the increase in interest in this species of betta and a greater understanding of its plight, the wild Beauty of Brunei may very well be well on the way to seeing a resurgence in numbers. 


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