Betta macrostoma, often called Brunei beauty is one of the most popular moutbrooding wild betta fish. Its bright orange colouration and relatively easy care make it a good choice as aquarium fish. However, there is a little more to this fascinating betta than to the classic domestic Betta splendens.
Betta macrostoma in the wild
Betta macrostoma lives on the island of Borneo in the Belait district in Brunei and in northern Sarawak in Malaysia.
Its wild habitat consists of jungle and dense vegetation and lives in streams and pools. The water is rather shallow, around one to two feet deep. In contrast to the habitat of well-known Betta splendens complex species living on mainland Asia, these pools usually have some form of current in them.
They are often found in small and slow flowing rivers with less or no vegetation in the water, which made them forced to use another way of breeding.
The substrate is made of organic materials, mostly leaves which causes a low pH. On catch sites, the pH on catch sites is between 4.4 and 5.7. This makes Indian almond leaves for your betta necessary to create a natural setup. The leaves and branches on the bottom provide shelter from predators.
Not many other fish except other Betta species such as Betta akarensis. However some shrimp species are living together with Betta macrostoma. Some people claim the red shrimp cause it to take on an even brighter more red color. This might be replicated with feeding cherry shrimp to your Betta macrostoma.
Betta macrostoma has been marked vulnerable on the IUCN Red List. Agriculture and wood-harvesting endanger the natural habitat of Betta macrostoma and cause rapid decrease in wild populations. Catching wild specimens to sell to the western aquarium trade has further decreased wild populations.
In Brunei, the species has been banned from export and catching in the wild. Any specimen sold as wild caught from Brunei is illegally caught. Most specimens sold are captive bred or wild caught out of Sarawak, where Betta macrostoma isn’t protected by law. To preserve this species in its natural habitat, purchasing captive bred specimens is best.
Betta macrostoma temperament
Betta macrostoma is a rather calm and peaceful betta compared to Betta splendens complex species. Once paired up, a male and female can live peacefully together. Unlike Betta imbellis that isn’t really peaceful, this species can be kept in pairs or small groups
Males can be aggressive and territorial towards each other to fight over dominance. If you keep multiple males together these small fights and flaring sessions are common but in a tank that’s big enough this isn’t a problem.
Two Betta macrostoma males and a female flaring over dominance.
Appearance of The Brunei Beauty
Betta macrostoma isn’t called Brunei Beauty for nothing. Its bright orange color makes it appealing for the eye and very recognisable. What makes it different from the well known species such as Betta splendens is that their fins are more modest and do not have these expressive fins to flare with.
What is very remarkable and one of the first things you see when looking at Betta macrostoma is their big mouth. In fact, its scientific name is derived from ‘macro’ which means big and ‘stoma’ which means mouth.
They use this big mouth primarily for breeding purposes and can handle bigger prey due to this advantage. When males flare, they will open their mouth as far as possible to impress the opponent.
Black markings are present on all fins. On the cheek scaling there is one black vertical marking and the mouth is fully black.
Betta macrostoma Care
The care of Betta macrostoma is different from the care of other betta species such as the domestic Betta splendens or bubble-nesting wild bettas. Especially their housing and behaviour to each other.
While most other bettas can live in small 5 gallon tanks, it’s recommended for Betta macrostoma to be kept in a tank of at least 20 gallons long.
Betta macrostoma is best kept in pairs and male and female will be peaceful towards each other once paired. A 20 gallon tank gives the pair enough space to have their own spots, and if there are small conflicts both can back off to another part of the tank.
Sometimes a male and female don’t get along with each other and can’t be kept together. To increase the chance of forming a successful pair you can form a group of multiple females and males. The fish will naturally choose their partner and later you can seperate them.
This is not always possible however and if you buy a pair from a breeder, ask if it’s living together and successfully paired. If it isn’t, pay attention the first weeks. Some aggression is normal when a pair is forming, but when both are constantly fighting it isn’t a good sign and they should be separated.
Plants and hiding material
Plants are the most important thing in your wild betta tank. They filter the water and add oxygen, which is beneficial for the biological balance and health of your fish.
More importantly, they provide useful shelter and a natural environment where your fish can feel safe. Especially if you plan on keeping Betta macrostoma in a pair or group, natural cover is necessary to provide spots where hide from each other in a conflict.
I would recommend live plants, since they contribute to water quality and just feel and look more natural. Your fish will certainly notice the difference. Some good plants that thrive in low-light setups and don’t need a lot of care are Anubias, Java fern, Java moss, Cryptocoryne wendtii and floating plants such as frogbit.
To provide some extra hiding spaces and add an extra natural touch while improving the depth and aquascape, hardscapes are a great cover. In the wild betta habitat of Betta macrostoma there are tons of fallen trees and branches that provide places to reproduce and hide.
All kinds of driftwood and stones are good. If you add stones, make sure they don’t contain chalch since it will increase your pH. Wood can lower your pH, but only a little bit compared to catappa leaves, that contain a lot more acids and tannins.
Filter and lighting
Betta macrostoma prefers a low-light setup. The chance on your Betta macrostoma getting stressed is higher. Especially wild betta fish, that aren’t as adapted to captivity as the domestic betta are more sensitive towards bright light.
Floating plants are great to lower the intensity of your light and provide cover at water level. My favorite floating plant is frogbit. They grow very fast and thrive in most tanks. They have long roots that provide extra shelter.
Other plants like Echinodorus have big leaves that create shadow under water and places where your fish can hide.
It is advised to have some sort of current in your tank and I find Betta macrostoma does well with some natural filtration. Filters that filter your water volume 2-3 times an hour are a goed choice. Having too much current does more harm than having too little, so experiment with how your fish behave with faster flowing water.
Great cheap filters that provide biological filtration are sponge filters, that work on air provided by an air-pump.
Betta macrostoma feels most comfortable in small groups or pairs without other fish. However, if you have a bigger tank and feel your tank is a little empty with only your Betta macrostoma, you can add some calm small fish species.
Bigger fish such as for example gouramis are too aggressive and will compete with your Betta macrostoma. This causes stress for both species and it’s recommended to only have one dominant species per tank.
It’s possible your Betta macrostoma will occasionally eat or attack some of the smaller fish, so be prepared for that.
To make a good choice for which fish to put with your Betta macrostoma here are some small fish that go well in most setups. This is no guarantee that it will work, but with the good setup your Betta macrostoma should be able to live together with some tank mates.
Otocinclus – Otocinclus are peaceful algae eaters living in South America. They live in the middle layer and stick to the cover and plants. They will not annoy your Betta macrostoma and eat plant based foods and algae.
Corydoras – Corydoras are great and peaceful catfish that live on the bottom of the tank feeding of leftover food. They have the same diet as Betta macrostoma, so you will need to feed some extra so the corydoras get some too. Small species of Corydoras are C. habrosus and Corydoras that go well in groups of 5-10 fish.
Harlequin Rasbora – Trigonostigma heteromorpha is a fish species that naturally occurs in the wild habitat of betta fish (Southeast Asia). They are small and calm fish that swim at the middle-upper layer of the aquarium. A small group should be able to peacefully coexist with Betta macrostoma.
Kuhli loach – Kuhli loaches are similar to Corydoras in terms of care. They live on the bottom and are a rather shy and very peaceful species. Khuli’s are big enough and fast so your Betta macrostoma will not be able to eat them.
Some sources claim Betta macrostoma is omnivorous. This is not true and Betta macrostoma eats only meat-based foods which makes them carnivorous. In the wild betta fish mostly eat different kinds of insect larvae such as mosquito larvae. Other things they eat are flies and worms.
If you look at the mouth of Betta macrostoma it’s obvious that they don’t stick to the innocent insects. They also eat small fish and shrimp and will take everything they can swallow.
The best is to feed them a variety of different foods so they receive all the nutrients and minerals they need. Live foods are the best, but frozen foods are a good alternative too. If you choose dried foods, always high-quality pick pellets that only contain meat. Flakes usually have more fillers in them which are bad for your fish’s digestion.
Betta macrostoma is more sensitive towards water parameters than most other Betta species. It is very important that your water parameters are stable and don’t fluctuate a lot with water changes. If your tap water contains a lot of unnatural chemicals or harmful chemicals, it’s recommended to use RO water.
In its wild habitat pH can get as low as 4.4. Betta macrostoma will benefit from lower pH, although captive bred fish are more used to higher pH. In your tank, I recommend having a pH of 6-7.
You can lower your pH with natural materials such as Indian almond leaves or peat moss, if your KH is low enough.
Temperature isn’t very different from normal betta fish. You can keep them at a temperature between 74°F and 80°F.
Natural leaves such as catappa leaves (see above) or alternatives like alder cones add natural tannins to the water that improve your water and benefit your fish’s health.
Breeding Betta macrostoma
Breeding Betta macrostoma is very exciting, and more easy than you’d think. If you keep your Betta macrostoma in pair(s) there’s a good chance your bettas spawn naturally without any extra attention.
Betta macrostoma is a mouthbrooder (how could they not be with such a mouth). This means that they don’t build bubble nests such as Betta splendens, but that the male incubates the eggs in his mouth.
You will only be able to spawn if your pair is already formed before spawning. Unlike domestic bettas which you can spawn bettas that have never seen each other, Betta macrostoma needs to be paired first.
The best way to successfully pair Betta macrostoma is by keeping them in a group. In a group, multiple pairs will naturally form and later they can be separated for breeding. If you only want to keep one pair, you can sell the pairs individually later on.
For breeding Betta macrostoma you don’t need any extra breeding setup. You can perfectly spawn them in the tank where your pair already lives in. However if your pair spawns it is hard to raise the fry in the main tank. To have more control about the breeding process and the development of the fry you can set up a separate tank.
A breeding tank can be smaller than your main tank, but has to be at least 15 gallons to make sure your fish can avoid each other when there are fights.
To increase the chance of success, the water level can be brought to 20-30cm. This makes your tank more natural.
Add a lot of plants and catappa leaves to provide hiding places. Dim the lighting to reduce the possibility of your pair getting stressed.
A filter isn’t really needed in the breeding setup, since your Betta pair will only live there temporarily and it can be a source of stress for the male. After your fry is released by the male, it’s recommended to add a filter to filter out waste that is being produced by the fry.
If your fish don’t seem to spawn naturally, you can condition them to encourage spawning behaviour. You do this by feeding them live foods for multiple weeks to encourage the female to produce eggs.
Placing them over to a dedicated breeding tank with a lower water tank and lots of natural tannins usually causes breeding behaviour. Some sources claim that lowering the pH can encourage spawning as well.
Spawning and caring for the fry
The spawning process takes a couple of hours on average, where the male and female wrap around each other. They will dance around each other and both will color up more. The female lays the eggs and the pair wraps around each other so the male can fertilize the eggs.
Usually the female picks up the eggs and passes them to the male, that will care for the eggs and fry.
On average a batch contains between 15 and 30 relatively big eggs. Betta fish eggs of the domestic betta usually take only a couple of days to hatch. Betta macrostoma eggs take way longer, between 15 and 30 days to hatch, depending on various factors such as water temperature and quality.
After this the male will care for a couple days for the fry. After this the fry is free swimming and should be fed baby brine shrimp.
It is possible that the female doesn’t pass through the eggs to the male and that the spawn is lost. More common is that the male eats the eggs or that the eggs aren’t fertilized. Mostly inexperienced males will eat eggs due to stress caused by other fish or the environment.
To decrease the chance of your male eating the eggs leave alone the pair and don’t feed the male while he is holding eggs. You can cover the glass with foil and dim the light to give the male all the rest he needs.
After the male has released the fry, you should take out the pair out of the breeding tank so they don’t eat the fry.