Betta Macrostoma Care: Tank Mates, Breeding & Diet

Not to be confused with the more common Betta splendens, the Betta macrostoma is a rare and exotic breed of betta. While they’re in the same family, there’s a huge difference in care and difficulty when it comes to these fish.

And you’ll have to overcome some sticker shock just to get started.

But let’s dive right in, and I’ll show you the basic tenets of caring for Betta macrostoma and how to make them thrive in your tanks!

Betta Macrostoma

Betta Macrostoma Quick Care Sheet

  • Common Name: Brunei Beauty
  • Alternate Common Name(s): Spotfin Betta, 
  • Latin Name: Betta macrostoma
  • Care Level: Advanced
  • Tank Size: 10 gallons +
  • Size: 4 ½”
  • Diet: Carnivorous*
  • Behavior: Semi-aggressive
  • Lifespan: 3-5 years
  • Reproduction Type: Mouthbrooder
  • Water Temperature: 75-80°F (24-27°C)
  • pH: 6.0-7.0
  • Water Hardness: 1-10 dKH

Origins of the Betta Macrostoma

Betta macrostoma is the holy grail for serious Betta collectors. These fish are rare, expensive, and require way more attention than the commonly sold Betta splendens.

These brilliant fish are larger than normal Betta, ranging from 3 ½–4 ½”. The size difference means they require a larger tank than Betta splendens, I recommend at least a 10 gallon for a single Betta macrostoma.

These fish occur in a very specific environment in Brunei, with a smaller occurrence of the species in the very northern tip of the Malaysian state of Sarawak. The latter is the only legal collection spot for this species, those that are contained in Brunei’s borders are illegal to collect.

They inhabit still pools along the riverbanks, and a single still spot is often the place that a Betta macrostoma will call its territory. Like Betta splendens, the males are extremely hostile with each other and it’s impossible to keep more than one in the same enclosure.

The fish are otherwise pretty sedate, being a bit calmer than B. splendens. It’s much easier to keep a mated pair of these fish together than you’ll find with most species.

The Brunei Beauty is usually red, sometimes with a bit of blue, and has a sleeker body than B. splendens. They also lack the prodigious fins that make up the various B. splendens variants, they don’t even approach the “standard” veil tail, being much closer to the wild-type Betta.

Their latin name indicates one of their other apparent qualities: macrostoma roughly translates to “big mouth” and they’ve got that one covered.

There’s only one other fish that occurs in the same area. A Rasbora species that hasn’t been the subject of many studies, and a single red shrimp species that inhabit the bottom.

The water that B. macrostoma hails from is very acidic, with a pH as low as 4.7, and has almost no dissolved minerals. This combination of traits is hard to mimic with tap water in most locations, and you may want to invest in a reverse-osmosis system for your home water supply to make water changes and maintaining parameters easier.

You can already see that the set of challenges in front of you is much bigger than just picking up the fish. The Brunei Beauty isn’t the hardest fish to keep, but they are expensive and require some knowledge.

But first, we have a couple more things to talk about: ethical sourcing and some alternatives.

The Endangered Status of the Brunei Beauty

Unfortunately, these fish are on the IUCN red list, currently listed as “Vulnerable.”

There is no legal protection for the fish in Malaysia. Fish could potentially be caught there legally and sold into the aquarium trade. On the other hand, the fish is under intense legal protection in Brunei.

The problem is that many of the fish sold in Sarawak may have been poached in Brunei before being brought to Malaysia.

Wild-caught specimens appeal to some collectors, but in this case, I don’t feel it’s an ethical route. These fish are easily bred in captivity and captive-bred specimens are available. I suggest finding a reputable breeder if you’re interested in B. macrostoma.

When sourcing one of these fish, opt for captive-bred fish. The specimens will be cheaper, hardier, and don’t carry the baggage that illegal poaching creates for them in the wild.

Alternatives

B. macrostoma is a hard fish to keep, but its unique beauty often draws people to it. They’re also expensive. They’re among the most expensive freshwater fish, although they’re still cheaper than some oddballs and breeding pairs of Discus.

There are a couple of species that are similar but cheaper to buy and easier to care for.

  • Betta channoides– Another mouthbrooding Betta. B. channoides shares the breeding habit and coloration of the Brunei Beauty but is much more tolerant of water conditions. They tend to be a bit “chunkier” than most Betta species but they’re relatively easy to care for.
  • Betta albimarginata- A mouthbrooding, small Betta species with a streamlined body. They often share the same coloration, but they’re much more slender and only reach a length of about 1 ¼” at most.

These species are more common and cheaper, but they’re still listed on the IUCN list. Try to acquire them as captive-bred specimens.

Ideal Tank Setup

Fortunately, while the fish are rare and expensive, setting up their tank is easy. You just need to make sure that you have everything in order before you decide to introduce your B. macrostoma to the tank.

Recommended Equipment

Due to their natural environment, you’ll have to be careful with equipment. While they require very clean water, you also need to make sure that the flow rate isn’t too high or it can disrupt the fish. They come from rather still waters, after all.

You’ll need the following to get the tank setup properly:

  • Sponge or Canister Filter- Aim for the rated capacity of the filter. So a 10-gallon filter for a 10-gallon tank. That’s half the filtration I normally recommend. Make sure that the filter media can be fitted to your liking. You may need to remove the activated carbon depending on your water chemistry.
  • Heater- Reliable and rated for the tank. Spend a little bit more than normal and get something good. B. macrostoma is too rare and expensive to risk problems by saving a couple of dollars.
  • Lights- These fish seem to prefer a low-light environment. Aim for 1W or 50 Lumen per gallon, or just a bit more. If you prefer high lighting plants, you’ll need to invest in some floating plants to keep part of the tank shaded.
  • Nutritious Substrate- Something that has nutrients for the plants is recommended. The usual brands are all great, just make sure to rinse to avoid clouding. I also recommend sand if you’re planning on adding bottom feeders to the tank.
  • Hardscape Elements- Driftwood or rocks to tie plants to and create caves for the fish to explore. They’ll spend most of their time at the top level of the tank so you can get as creative as you’d like.
  • Plants- A lot of them. We’ll discuss some great options for those without a green thumb in just a moment, but the main consideration is density for extra nutrient absorption.
  • Leaf Litter- Using leaf litter is a great idea when keeping these fish. If you’ve never done it before, we’ll discuss it below!

It’s not an advanced setup overall, but focusing on making sure you’re using a high-quality filter and heater is a great idea. While it’s never fun to lose any fish to an equipment failure, it’s also expensive if you have a runaway heater or a filter that stops functioning while you’re not home.

Sponge filters are a solid choice for this tank. They provide quite a bit of filtration for a low cost and lower flow. That said, Bettas are all labyrinth fish so you don’t need the air bubbles. You can use a HOB if you prefer the water to look less disturbed.

While it’s not required to go with a low-light setup, it saves money and allows you more freedom in plant choice. A tank that’s highly lit still needs an area with a lot of shade, allowing your Brunei Beauty to hide for a bit if it likes.

Bottom line is that you only need regular equipment and moderate lighting to make these fish thrive.

Using Reverse Osmosis Water

Due to their recommended parameters, it’s best to use RO water to create a good environment for these fish. The RO process strips most minerals out of the water that passes through the filter, creating a great base to alter the water’s parameters.

For smaller tanks, you can usually get away with buying it by the gallon from the grocery store but that’s not a viable option in tanks 10 gallons or larger. In this case, you may want to see what you can do about getting a filter installed in your sink if you don’t already have one.

RO water naturally has a pH of 7 when it comes out of the tap. This lowers when exposed to air, reaching 5.5-6.5 quickly. That gets you most of the way there with your tank, and you may not need to alter the water further.

More importantly, it lowers the hardness of the water. The regions that the fish are native to have a negligible hardness and an acidic pH between 5 and 6. In some areas, the pH gets even more acidic, but it’s not ideal for keeping the fish in captivity.

The important thing is that the water going into your tank is acidic and low in dissolved minerals. Reverse osmosis filters are just the fastest way to get there, and in some areas, the tap water won’t be suitable without a lot of chemical modification.

Fish that have been captive-bred for a few generations are much hardier, and may be able to go in regular dechlorinated tapwater. That just gives you another reason to make sure that your fish has been bred domestically.

My insistence on water conditions applies primarily to wild-caught specimens. That said, it’s still good husbandry to keep fish in water that’s closer to their conditions in the wild.

Leaf Litter

Leaf litter will add tannins to the water column and create a stabilizing effect. It will also support the growth of infusoria, tiny critters similar to zooplankton in the ocean.

Using commercial leaf litter is the best idea for a newbie. Some leaves are safe and others aren’t when you’re looking at random trees and… this isn’t the time to experiment.

The litter will break down on the bottom of the tank over time and may need to be replaced, although some keepers will simply leave it. It’s “exhausted” when the litter has become a mush for the most part.

Keep in mind that leaf litter will make the water a bit brown. If you’re not looking to work with a black water tank, where the water loses some clarity, you may want to skip this step. Still, it’s one of the best ways to replicate the natural system of the Brunei rivers where wild B. macrostoma live.

Plant Recommendations

You have two main options when it comes to your plant choices.

Biotope aquariums are beyond the scope of this article, especially considering the lack of available information on the plant life of Brunei. Deeper research will be required, but you can find some bits of information to guide you along the way.

Or you can focus on plants that will help clean the water column with little consideration for their natural environment.

Your Brunei Beauty doesn’t really care which species of Cryptocoryne is in the tank.

I suggest fast-growing, low-light plants to fit the fish’s required environment. The good news is that there are a ton of these available commercially. Beginners kill a lot of plants, and your local LFS will stock a lot of beginner-friendly plants to make things easier for those who haven’t yet acquired an aquatic green thumb.

The following are solid choices for someone who doesn’t know where to start:

  • Java Moss- A versatile, nearly invasive plant. Java moss can be tied to hardscape, pushed into the substrate, or just allowed to float and create a shaded area. It’s nearly impossible to kill, but it’s also nearly impossible to remove from a tank once it’s been planted.
  • Cryptocoryne wendtii- The easiest of the Crypts to grow. While virtually unkillable as long as they have nutrients available, they melt when water conditions are changed. Your plants will likely appear to be dying when introduced to the drastically altered environment of a B. macrostoma tank but they’ll regrow.
  • Anacharis- Anacharis is easily found and the stems can be planted or floated depending on your choice. They grow very quickly and absorb a lot of nitrates and other problematic chemicals in the water. They require frequent trimming.
  • Hornwort- Hornwort is less problematic than normal when you’re using leaf litter as a substrate. It grows very quickly and it can be allowed to grow floating to create shade.

There’s one other plant that can help with these fish but it’s a very personal choice. Duckweed can usually be found at most pond or fish stores. A good percentage won’t charge you anything for a few bits to get a colony started. 

I actually have to comb the water from my favorite LFS to remove it before adding new plants to keep it from ending up in my aquaria.

That said, it has some serious drawbacks. It can take over the top of a tank in just a few days and requires constant thinning. A fishnet is fine to thin it out, just scoop until you’re happy with what’s left.

It’s also an attractive feature in moderation and it grows densely enough to provide shaded areas for the fish.

In addition to the above, any plant you can keep alive in acidic conditions is a good choice. The focus here is on shade and fast growth to keep the water column clean.

Cycling the Tank

Betta macrostoma should never be placed in a tank that hasn’t been cycled. They’re sensitive to water quality and won’t survive a cycle in most cases. Expect to spend a couple of weeks leveling the tank out before you add them.

Cycling is a simple process:

  1. Set up your tank as normal, including equipment, hardscape, and plants.
  2. Add a small amount of fish food daily, a tiny pinch of flake will work.
  3. Test the water for ammonia daily.
  4. Once ammonia is detected, keep testing 1-2x per day until ammonia hits 0ppm according to your test kit.
  5. Now test for nitrites in the same manner, it’ll usually flag the test for 2-3 days before dissipating as the bacteria colonies grow.
  6. Check for nitrates daily, wait until they’re at a low level (<15ppm, ideally <10ppm) before adding your fish. Make sure the level is stable for a couple of days.

You may be able to get away with higher nitrates than indicated above, but I don’t recommend it. These fish are a serious investment and breeding programs are required to keep the wild population safe. 

Each of these rare fish dying is a bit of a tragedy. Sticking to the above guidelines and making sure you have soft, acidic water will go a long way towards ensuring the fish will live through its natural lifespan.

Specialized Care Requirements

The main downfall of would be Spotfin Betta keepers is in their setup. They end up in a tank that’s not cycled or doesn’t have the proper parameters to maintain their health in the long term. If you’ve been careful up to this point, the rest will be easy.

Like all fish, however, there are some tricky bits of their care that you need to be aware of.

Feeding Time

B. macrostoma is a carnivore. I’ve seen them listed as omnivorous at times, but it’s not true.

Feeding wild-caught fish is always difficult. Most Betta macrostoma will learn to eat frozen foods eventually but things like flake and pellet will be ignored. Some captive-bred specimens can be taught to eat the usual suspects, but there’s no guarantee.

For the best results, always keep frozen food on hand. Bloodworm and beef heart are both great for keeping the fish’s coloration bright. Unlike B. splendens, which primarily eats insect larvae, these fish will eat smaller fish and invertebrates if they can as well.

You should also consider breeding daphnia or brine shrimp as live foods. Live food is a safe bet even for the wildest of fish, and it helps keep the fish occupied. Like all Betta, B. macrostoma is a lot smarter than they’re given credit for. A bit of work isn’t going to hurt them.

Daphnia cultures are readily available, and their care isn’t difficult. Brine shrimp aren’t much harder to take care of.

The point is that you may have trouble getting your Brunei Beauty to eat. Be prepared and have the cultures on hand before you bring the fish home.

Suitable Tankmates

I recommend just keeping a pair of B. macrostoma with no other fish. Those that you do add should be bottom dwellers. They can also survive alongside some of the calmer schooling fish… but they may eat them if the size difference is too large.

The following are, in my opinion, the best choices to keep with these fish:

  • Corydoras Catfish- Peaceful, active, and great at cleaning up any food that’s been missed by your Betta. They tend to school as the same species, so stick with one. Pygmy and Dwarf Corydoras aren’t good choices, they’re simply too small.
  • Otocinclus Catfish Otos are great fish and thrive in roughly the same environment. Otos have their own set of problems, but they can be fixed by only adding them to a tank that’s been established for a few months.
  • Cherry Barbs- Peaceful mid-dwelling fish that fit in well. Juveniles may be eaten by a full-grown B. macrostoma, so try to purchase adults or full-grown fish.

I prefer to keep bottom feeders in all of my tanks, but you may be best off just having a mating pair of these fish without any other companions.

Snails will usually be safe, or at least out-breed the rate they’re devoured at. Ramshorns and pond snails are readily available, and Malaysian Trumpet Snails will till the substrate constantine while remaining hidden.

You can also try housing them with a dwarf shrimp species. I recommend some variety of Neocardinia davidii, or Cherry Shrimp, since they’re cheap and breed quickly. With enough plant cover and a dozen shrimp per 5 gallons, you should be able to create a sustainable breeding population.

These aren’t community tank fish. You should be ready to remove and rehouse any fish you add to their tank at a moment’s notice. That said, you’ll usually encounter no aggression issues with calm fish that aren’t small enough to be eaten.

Betta macrostoma aren’t psychotically aggressive with other males, unlike the more common B. splendens. That said, the males are still rather aggressive with each other and you should plan to have at least 10 gallons for each male in the tank.

If you’re new to these fish, a single pair is your best bet for long term care.

Breeding Betta Macrostoma

Breeding these fish is a good thing. They’re endangered in the wild and poachers still threaten them. B. macrostoma are valuable enough that many criminals find it worth the risk to collect them in areas where the collection is illegal.

It’s also a good way to make back the money from your upfront investment. These fish are highly sought after, and often the market doesn’t have enough of them for the demand.

A single breeding pair should be kept in a 20 gallon long or larger tank. It requires a bit of space. You may also want a separate breeding tank, where you can keep the fry separate from their parents as they begin to grow out.

Most of the time a breeding pair will start mating before you need to do any conditioning. If that’s not the case, then you’ll need to try some conditioning techniques to trigger them.

The following all work well:

  • Dropping the level of the tank to 12” better simulates their natural environment.
  • Using a breeding tank with a leaf litter bed can also help, especially if their primary tank doesn’t have leaves.
  • Lowering the pH a little bit is sometimes effective, but rather risky if you’re not 100% sure of what you’re doing.
  • If your tank has high lighting, you may need to switch to a bulb with less output until the fish have spawned.

I recommend using a dedicated breeding tank if you’re looking to alter the water level or water chemistry. It’s not a great idea to start modifying parameters in a tank where the fish are already healthy due to their touchy nature.

The following information should help you run a successful breeding program, but I strongly encourage you to stay in contact with other breeders. There’s always room for improvement when it comes to keeping fish.

Sexing Betta Macrostoma

Sexing these fish is easy, like most Betta species. The male is a bright red coloration and has larger fins. They’ll look their best when breeding, but a healthy B. macrostoma will be scarlet at all times.

The female usually bears two lateral lines in addition to the other signs of sexual dimorphism. Confusing the sexes with this species is hard, you’d have to make a deliberate error if you know enough to be keeping them.

Pairing Fish

Most people buy their B. macrostoma in breeding pairs. They’ll usually bond quickly, and it’s the best way to begin a breeding operation for these fish.

The problem here is that these fish have to pair off with one of the opposite sex to breed. With most Betta species, you can simply place a male and female together and they’ll get down to it. Apparently the Brunei Beauty needs a little bit more romance.

If you have fish that aren’t paired, they’ll mostly just be a bit aggressive with each other. The male has to choose a mate. Trios are a common way to make sure that the fish are ready to breed.

Given enough space, you can actually keep a school of these fish in a larger tank (ie: 55 gallons or more) and let them pair off naturally. Just make sure to watch the males for aggression, as they’ll occasionally have violent disputes.

If you don’t have at least one pair… you don’t have a breeding program. The fish pair off quickly when given the opportunity, but a newbie will be better off buying a pair that’s already bonded.

Courtship and Spawning.

Spawning is triggered by having paired fish in good conditions.

The actual spawning takes some time, but you’ll have a good indication when you see the fish “dancing” at each other. Both sexes do a bit of a dance, with a lot of fin flaring and other showy moves, and the male opens his mouth very wide.

At some point, the male will make almost a complete circle around the female to squeeze out the eggs, which leaves him motionless on his side for a moment.

The female does her best to gather all of the eggs with her anal fins. The eggs are quite large, and even those that reach the bottom of the tank are usually picked up during the process. The male will pick up some on his own, but the female usually gathers some in her mouth and “spits” them towards the male. This “kissing” action helps the male gather them in his mouth.

Once that’s done, you may want to remove the female from the tank. The male needs as much peace as possible for the next stage.

Mouthbrooding

The male won’t eat for about a month while he incubates the eggs in his mouth. Otherwise, he runs the risk of eating the eggs as well. He’ll be fine, but tired, after this period.

The fry are about a quarter of an inch long and will begin hatching after 30-35 days.


The important thing is to make sure the tank is stable and peaceful while the male is brooding. That may mean removing the paired female, but you may want to place the breeding tank somewhere out of the way if you have a busy home.

Raising the Fry

As long as there’s peace and stable water chemistry, you’re good to go. The fry should be kept in the breeding tank and your focus should be on providing small live food (ie: infusoria, baby brine shrimp, daphnia) and not letting the water conditions waver.

The fry are even more sensitive to bad water chemistry than the adults. Do smaller, more frequent water changes than you normally would and test the water regularly.

You’ve got about two months to figure out how to house the babies. At that point you’ll be able to sex the fish, and the males will begin to get aggressive with each other. Manage that aggression by moving them to different tanks.

Fortunately, you won’t have hundreds of fry after the process. Betta macrostoma only lays 15-30 eggs. If you’re anything like me, the main problem you have when breeding is housing hundreds of fish before they reach their end home.

A couple of extra 20 gallons with bare bottoms, cycled filters, and a lot of floating plants make excellent temporary housing. You have time to start them after the mating process, but I’d try to make sure each has been cycled and stable for a month before adding the fish.

Your main problem with upkeep is going to be water quality. You have to be aware of overfeeding and any possible changes in water chemistry that can occur.

Just keep using your test kit. Aquarium testing kits are under-utilized by most of us, but with these fish you’ve got a lifesaver contained in a few little vials and dropper bottles. pH is the quality most likely to swing and cause problems.

Rehoming these fish is very easy, especially if you’re offering bonded pairs.

Outbreeding

You’ll want to outbreed regularly to avoid problems. Most recommend doing so every third or fourth generation.

This is more important than when you consistently inbreed something like guppies. The Betta macrostoma in captivity have a shallow gene pool. The fish’s tiny range in the wild and the relative lack of breeding programs can lead to recessive genes doing irreparable damage to a line.

The best way to find fish to outbreed with is to get in touch with other breeders. You may even be able to convince them to just trade pairs straight across, which is much more attractive than spending $200+ on another breeding pair.

The King of Betta

Betta macrosoma is a challenge for most keepers but one that can easily be conquered with the right information. These fish are some of the most sought-after Betta species, the holy grail for those who collect wild-type Betta. Their care is exacting, but not truly advanced, and a breeding program is well within the reach of most aquarists.

So, good luck on your journey! Just remember to never stop learning about these amazing fish.