Betta Macrostoma – The Crown Jewel of Brunei

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Betta macrostoma, also known as the Brunei Beauty, is an enigmatic species of Betta fish that has captured the hearts of fish enthusiasts around the world.

Known for its unique appearance and interesting behavior, this remarkable fish is an incredible addition to any hobbyist’s collection.

In this blog post, I’ll explore the origin and history of Betta macrostoma, its natural habitat, appearance, temperament, and everything you need to know about caring for and breeding these stunning creatures.

Origin and History

The fascinating history of Betta macrostoma can be traced back to the island of Borneo, which is the third-largest island in the world and is shared by three countries: Brunei, Indonesia, and Malaysia.

The species is specifically found in the northern part of the island, within the territories of Brunei Darussalam and the Malaysian state of Sarawak.

Betta macrostoma was first discovered in the early 1930s by British explorer and naturalist Charles Hose.

He stumbled upon the species in a remote area of Sarawak and sent preserved specimens to the British Museum in London.

However, the fish remained scientifically undescribed until 1953 when ichthyologist Tyson R. Roberts, who specialized in Southeast Asian freshwater fish, formally described the species and established its taxonomic position.

The unique features and behaviors of Betta macrostoma were not widely known in the fishkeeping world for several decades after its discovery.

This is mainly due to its limited distribution and the challenges of collecting and exporting these fish from its remote natural habitat.

It wasn’t until the late 20th century that Betta macrostoma began gaining recognition among fish hobbyists, primarily in Europe and the United States.

The increasing popularity of Betta macrostoma, along with habitat destruction and pollution, has put pressure on wild populations, leading the IUCN to list the species as vulnerable.

In response to this conservation concern, several captive breeding programs have been initiated by dedicated hobbyists and conservation organizations.

This is to preserve the genetic diversity of the species and reduce the demand for wild-caught specimens.

Natural Habitat

The natural habitat of Betta macrostoma is situated within the lush rainforests of Borneo, one of the world’s most biodiverse regions.

These rain forests provide a unique and complex environment that supports a vast array of plant and animal species.

Betta macrostoma is primarily found in slow-moving blackwater streams and peat swamps in the lowland rain forests.

Blackwater streams are characterized by their dark, tea-colored water.

This is the result of tannins and other organic acids leaching from decomposing leaves and plant matter on the forest floor.

These tannins create a soft, acidic environment with low mineral content, which is essential for the well-being of Betta macrostoma.

Peat swamps are another key habitat for Betta macrostoma.

These swamps are formed by the accumulation of partially decayed plant material in waterlogged conditions, creating peat deposits that can be several meters deep.

Peat swamps also have dark, acidic water with high levels of dissolved organic matter, making them an ideal environment for this species.

The dense vegetation in Betta macrostoma’s habitat provides crucial shelter and cover, allowing the fish to evade predators and find suitable nesting sites.

Overhanging plants, submerged tree roots, and leaf litter create a complex underwater landscape that offers numerous hiding spots and foraging opportunities.

The presence of aquatic plants, such as Cryptocoryne and Blyxa, contributes to the stability of the habitat and provides additional shelter for these shy fish.

The slow-moving waters of blackwater streams and peat swamps provide a calm environment for Betta macrostoma.

These fish rely on its large mouth and specialized gill structures to extract oxygen from the oxygen-poor water.

The reduced water flow also allows for the formation of bubble nests during the breeding process, as it prevents the fragile nests from being disrupted by strong currents.

Appearance and Size

The striking appearance of Betta macrostoma sets it apart from other Betta species, making it a sought-after addition to aquariums worldwide.

One of the most prominent features of Betta macrostoma is its large mouth, which inspired its name, derived from the Greek words “macros” (large) and “stoma” (mouth).

This unique adaptation allows the fish to capture and consume larger prey items, such as insects and small crustaceans, in its natural habitat.

Their elongated body shape is well-suited for navigating the dense vegetation and complex underwater structures found in their native environment.

The coloration of Betta macrostoma varies between males and females, with males being more vivid and striking.

Males typically exhibit a deep blue or black body, contrasted by a bold orange or red stripe that runs horizontally along their sides.

Their fins, especially the dorsal and anal fins, are elongated and adorned with vibrant red or orange edges, adding to their visual appeal.

Females, on the other hand, display a more subdued coloration, with their bodies usually featuring muted shades of brown or gray.

They also lack the distinctive finnage of the males, which allows for easy sex differentiation in mature fish.

Temperament and Behavior

Contrary to the aggressive reputation of their popular cousin, the Siamese fighting fish (Betta splendens), Betta macrostoma is relatively peaceful and shy by nature.

These fish tend to spend much of their time hiding among plants, roots, and other sheltered areas within their environment.

Their curious nature means they will often investigate their surroundings and interact with objects and other inhabitants in their tank.

While Betta macrostoma is generally less aggressive than other Betta species, they can still exhibit territorial behaviors, particularly among males.

Males may display posturing, flaring, and occasional chasing when confronted with other males, especially during breeding periods.

However, these interactions are rarely as violent or damaging as those observed in Betta splendens.

Females are usually more tolerant of one another, but they can also exhibit territorial behaviors in densely populated aquariums or when resources such as food or hiding spots are limited.

To minimize aggression, it is essential to provide ample space and hiding areas for each fish in the aquarium.

Water Parameters

To keep Betta macrostoma healthy and thriving in captivity, it is crucial to replicate their natural habitat conditions as closely as possible.

They prefer soft, acidic water with a pH of 4.0-6.0 and a temperature range of 73-79°F (23-26°C).

The water should be well-filtered, and the addition of Indian almond leaves or other tannin-producing botanicals can help create the desired blackwater conditions.

Tank Size and Setup

A minimum of 20 gallons (75 liters) is recommended for a pair of Betta macrostoma, with an additional 10 gallons (38 liters) per added fish.

A well-designed aquarium should mimic their natural habitat, incorporating plants, driftwood, and other elements to provide shelter, hiding spots, and territories.

Live aquatic plants play an essential role in creating a natural and comfortable environment for Betta macrostoma.

Incorporating plants that are native to their natural habitat, such as Cryptocoryne and Blyxa, can help replicate their blackwater stream and peat swamp surroundings.

Floating plants, like Salvinia or Frogbit, can provide shade and cover, as well as help to create a sense of security for the fish.

Dense planting will offer ample hiding spots, while also aiding in water quality by absorbing excess nutrients and providing oxygen.

Driftwood is another critical component in a Betta macrostoma tank setup.

Adding driftwood branches, roots, or stumps can create a complex and visually appealing underwater landscape that offers numerous sheltered areas for the fish to explore and hide in.

Additionally, driftwood can release tannins into the water, which can help to naturally lower the pH and replicate the soft, acidic conditions found in blackwater streams and peat swamps.

Providing caves and hiding spots is essential for the comfort and well-being of Betta macrostoma.

You can create these spaces using a combination of rocks, coconut shells, and commercially available aquarium caves or hideouts.

Arrange these elements throughout the tank to offer each fish a place to retreat when they feel stressed or threatened.

Ensure that any rocks used are smooth and free from sharp edges to prevent injury.

A dark, fine-grained substrate, such as sand or fine gravel, can help mimic the natural environment of Betta macrostoma and make the fish feel more at ease.

Dark substrates also bring out the vivid colors of the fish and create a visually appealing contrast.

Ensure that the substrate is smooth and free from sharp edges to prevent injury to the fish.


Betta macrostoma, like most Betta species, is predominantly carnivorous, consuming a diet of mainly insects and small crustaceans.

In captivity, it is important to provide them with a varied and nutritionally balanced diet to maintain their health, coloration, and overall well-being.

A significant component of Betta macrostoma’s diet should consist of live foods that closely resemble their natural prey.

Live foods, such as brine shrimp, daphnia, mosquito larvae, and small insects like fruit flies, not only provide essential nutrients but also stimulate the fish’s natural hunting instincts, promoting physical activity and mental stimulation.

In addition to live foods, frozen alternatives can also be offered to Betta macrostoma.

High-quality frozen foods, like bloodworms, mysis shrimp, and blackworms, provide a convenient and nutritious option that closely mimics the fish’s natural diet.

Thaw frozen foods before feeding them to your fish to ensure they are easily digestible and at an appropriate temperature.

While live and frozen foods should form the bulk of Betta macrostoma’s diet, specially formulated Betta pellets and flakes can be used as a supplementary food source.

These products are typically high in protein and fortified with essential vitamins and minerals.

However, they should not be used as the sole food source, as they do not provide the same nutritional diversity and enrichment as live or frozen options.

Suitable Tank Mates

Betta macrostoma prefer to be in a species only tank but if you want to add suitable tank mates then choose wisely to avoid them being eaten or attacked.

It is essential to choose small, peaceful species that share similar environmental requirements.

Fish such as Harlequin Rasboras (Trigonostigma heteromorpha), Ember Tetras (Hyphessobrycon amandae), and Celestial Pearl Danios (Danio margaritatus) make suitable companions due to their non-aggressive nature and preference for soft, acidic water.

Bottom-dwelling fish can be a good choice for tank mates, as they occupy a different area of the tank and are less likely to come into direct competition with Betta macrostoma.

Species like Corydoras catfish, Kuhli Loaches (Pangio kuhlii), and small Loricariid species (e.g., Otocinclus) can coexist peacefully with Betta macrostoma.

Species to Avoid:

Avoid housing Betta macrostoma with aggressive or territorial fish, such as other Betta species, Cichlids, or large Barbs, as these can lead to conflicts and increased stress for all inhabitants.

Additionally, avoid species that require significantly different water parameters, as this can compromise the health and well-being of both Betta macrostoma and their tank mates.


Betta macrostoma can be susceptible to a range of external and internal parasites, such as Ich (Ichthyophthirius multifiliis), velvet (Oodinium spp.), and gill flukes (Dactylogyrus spp.).

Symptoms of parasitic infections may include white spots, lethargy, loss of appetite, and rapid breathing.

To prevent these infections, quarantine new fish before introducing them to the main tank, maintain good water quality, and avoid overcrowding.

Bacterial infections, such as fin rot, columnaris, and dropsy, can affect Betta macrostoma if water quality is poor or if the fish are stressed.

Signs of bacterial infections may include frayed fins, ulcers, reddened areas, or swelling.

Maintaining good water quality, providing a stress-free environment, and feeding a balanced diet can help prevent bacterial infections.

Fungal infections can also affect Betta macrostoma, particularly if they have been injured or if water quality is poor.

Symptoms of fungal infections can include white, cotton-like growths on the body or fins.

Prevent fungal infections by ensuring good water quality, providing appropriate tank decor that minimizes the risk of injury, and quarantining any injured or sick fish.

Breeding Betta macrostoma

If you are planning to set up a breeding tank for Betta Macrostoma, there are a few important things to consider.

First, you will need a tank that is at least 20 gallons or larger with clean water and a pH level of 6.

The tank should be dimly lit with low water flow, and you should provide plenty of decor and live plants to create a safe environment for the fish.

Additionally, maintaining a slightly higher temperature will mimic their natural breeding season, which occurs in late winter and spring.

When it comes to the spawning process, the female Betta Macrostoma will start flaring and flapping its fins in front of the male.

The male will respond by opening its mouth wide, and the female will mirror this behavior.

The male will then wrap around the female in an embrace until its pelvic fin rests on the female’s mouth, which will stimulate the female to release her eggs.

The male will immediately fertilize the eggs, and then pick them up in his mouth.

The female will help by picking up the eggs and spitting them into the male’s mouth, often compared to a “kiss.”

During the incubation period the male will not eat and spend most of his time resting.

This will last for about a month.

It is crucial to maintain a peaceful environment during this time, as stress can cause the male to swallow the eggs.

If necessary, you can remove the female from the tank to avoid stressing the male.

After about 30-35 days of incubation, the Betta Macrostoma fry will be released.

They will be tiny and range from 0.2 to 0.3 inches in length.

Make sure the tank is heavily planted so the fry can hide and escape being eaten.

It will be a good idea to remove the parents to increase the survival rate of the fry.

To ensure the fry’s optimal growth and overall health, feed them microworms, vinegar eels, grindal worms, white worms, baby brine shrimp, and daphnia.

It’s important to monitor the water quality and temperature regularly, as fry are more sensitive to water parameters than adult Betta Macrostoma.

Fry also release growth-inhibiting hormones into the water, so regular water changes are critical.

A daily 10% water change is recommended. With proper care, the fry will grow rapidly, and at around two months of age, they will start to exhibit their colors.

Eventually, the males will start to show aggressive behavior toward each other, and you should separate or move them to a larger tank.

Why Should You Consider This Fish

Betta macrostoma is an extraordinary and captivating species that deserves a place in the aquariums of fish keepers who appreciate unique and beautiful fish.

With their stunning coloration, fascinating behavior, and intriguing breeding habits, Betta macrostoma offers a rewarding and engaging experience for both novice and experienced fish keepers alike.


Why are Betta Macrostoma so expensive?

These betta fish are very rare and are not easy to find. They are also under threat in their natural habitat. This is why they are so expensive.

What is the life span of a Macrostoma?

They can live anything between three to five years depending on water conditions and diet.

Are Betta Macrostoma aggressive?

Male Betta macrostoma can be aggressive towards each other but normally these fish do not bother other peaceful fish

Photo of author


Irma Bense is the founder of She has over 42 years of experience in keeping fish.She has kept both freshwater and saltwater fish through the years.She has extensive knowledge in breeding numerous species of fish from Show Guppies, Cory Catfish, German Blue Rams to Apistogrammas.You can learn more about Irma on the 'About' page.

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