Betta Macrostoma: Caring For & Breeding The Dream Betta

Betta macrostomas are the dream fish for nearly every betta enthusiast, but not every keeper should have them. On top of being threatened by heavy environmental and local strain, they’re also difficult to keep and find, making them a massive financial investment as well.

Because these guys are so susceptible to becoming endangered, the Sultan of Brunei has banned the species from export. In fact, there was a point from the 30s until the mid-90s where we thought they were completely extinct in the wild. Since their rediscovery, hobbyists have rushed to collect the once-thought-extinct fish, putting wild populations in more danger.

Most of the wild-caught fish are likely to originate from Sarawak, where the species is not protected by law. However, there is some speculation that fish are being smuggled illegally (poached, really) from Brunei to be sold in Sarawak and shipped to consumers. Because of that, I suggest buying only captive-bred species to protect the wild population, though captive-bred can be hard to find.

If you like the way they look, easier to care for, easier to find, and less expensive species would be Betta albimarginata or, easier still, Betta channoides. All three are paternal mouthbrooders, but B. albimarginata and B. channoides are both endangered, so they would still make a super rewarding breeding project.

If you have your heart set on keeping the holy grail of bettas, B. macrostoma, I’ll tell you everything you need to know about keeping, caring for, and breeding these rewarding beauties from Brunei.

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Table of contents

Distribution & Natural Habitat

Macs have been collected from still, shady pools at the top of rainforest waterfalls in both Brunei and Sarawak. The water is relatively fast-flowing (hence the tops of waterfalls,) with a slight brown hue from some sparse leaf litter. The substrate is usually varying sizes of river stones.

In a few other collection spots, the water is completely still. In these areas, usually in spots off the main river or tributaries, there was only one pair or several juveniles observed per location.

It can be found alongside Rasbora tubbi in some locations but is almost always found alongside a red species of Macrobrachium (sp.) shrimp, leading some experts to suggest it could be an integral part of their diet in the wild.

The loss of coloration and vigor of tank bred individuals seems to support this, perhaps lacking carotenoids or other essentials from the food they’re being fed. All that seems to come up is red Macrobrachium shrimp of Sarawak. I would assume the adults would be too large, but the babies would perhaps be the right size to prey on.

Aquarium Care

Betta macrostomas are often considered difficult to keep – and even more difficult to breed. But, the reality is, they’re not difficult to keep if you’re able to keep their parameters stable. The real challenge with this isn’t your natural water parameters, it usually comes down to how well you cycled the tank and consistent water change practices.

As far as breeding goes, getting males to “hold to term” can be challenging. Some males are more spookable than others and there aren’t a whole lot of reliable tricks to keep a male from swallowing the eggs or spitting out his fry early.

Tank Specs

You’re going to want a 20 long with a tight-fitting lid since they’re amazing jumpers. Bear in mind that if you’re planning on pairing them up, you’ll likely want something like a 40 gallon for quarantine or pairing as well as several 20 longs for the resulting pairs. Or – better yet – more 40-gallons for breeding so the fry can stay with their parents longer, resulting in less stress for everyone.

You’ll also want either a ton of 40s or a few 75s for raising the fry. 90s or 120s would be better, but they are both considerably more expensive and more difficult to find. (Particularly if you grab Petco’s $1/gallon sale!)

You’ll also want a heater, preferably with an alarm system. Even though macrostomas run cold, you’ll want a heater to keep things stable in their tank. An alarm system with an external control will provide you with even more stability (and peace of mind.)

I have all the best heaters in a complete article, but I’ve also plopped the winning heater and alarm system below if you don’t know where to start. I would say go on the side of 3 – 4 WPG for the heater just to make it super difficult to overheat their tank.

Stocking

They can be kept in a group, but do best in pairs for breeding. Both males and females will spar and squabble until a hierarchy is established and they’re paired off. Plus, you’re unlikely to find fry in a group situation. For the sake of safety (though few injuries usually result) it’s best to keep them in pairs once they’ve chosen their mate.

Your best bet is to purchase a group of juveniles and raise them together. If you can’t do that, you can purchase two trios or just one trip and hope for the best. Even when purchasing a group of juveniles, there’s no guarantee you’ll get a male. Only an estimated 10 – 15% of fry will be males.

Decor

If you plan on breeding macrostomas, you’ll want to keep it bare bottom for ease of maintenance. The addition of some leaf litter, caves, and plants that don’t need to be planted would also be appreciated.

Adding a dark background or painting three walls of the tank black will help them feel more secure as well. You may want to add some driftwood, but be aware of your skills with a net. Netting fry out of a tank with wood in it can be a chore.

Tannin Aquatics has some good leaf litter packs if you want some cool botanicals. Additionally, you can use PVC for caves, large terracotta pots with holes in them, or buy some open-ended premade caves.

Best Plants For Betta macrostoma

When looking for plants, you’re going to want to find plants that do well at lower temperatures, in acidic conditions, with lower lighting, and that don’t need to be planted in substrate if you plan on running a bare bottom (which I advise.) There are a few I can think of that would probably do well in those conditions.

If you can find fast-growing plants like guppy grass, hornwort, or water sprite, those would help keep your water cleaner as a bonus.

Sweet Potato

Water Wisteria

Java Moss

Guppy Grass

Lighting & Filtration

You’ll want to shade the tank without the addition of a ton of tannins. You can purchase smoked glass or a light with a dimmer to achieve this effect. I, personally, like the 24/7 lights for skittish fish because they won’t spook when they lights turn off or go out because it’s gradual.

Additionally, it’s worth remembering these guys come from areas of moderate flow with lower tannin levels. You’ll want something like an underrated HOB (2 – 3 GPH) with a sponge prefilter or a sponge filter with a water polisher (for circulation and tannin removal.) I suggest the latter because you can fine-tune the level of flow much easier, but a HOB with a prefilter would also fit the bill if that sounds more like your style.

If you can, my personal preference would be an HMF with a water polisher and spray bar. Everything could be hidden behind the filter, including the heater, for added protection. If you got black you’d hardly notice it was there. In either case, I don’t suggest buying a water polisher (unless you really want to,) most because they’re easier to make than they are to find.

As for the filters, I have some of my favorites below.

Water Care

You’ll want to change 25% of your water every week, if not more. Smaller daily water changes of 10% would be better, but if you can’t find the time every day, weekly, consistent water changes would be best. If your water is hard, you’ll likely need an RO unit to get your water to the right dKH by cutting it with your tap.

In addition to that, you’re going to want to stock up on some basic meds and water care necessities. Based on the most common illnesses macrostomas get, I included all the meds you should (reasonably) need below.

Feeding Betta macrostoma

Betta macrostomas won’t usually take dried foods (even if they’re captive bred.) But they’ll accept live foods and frozen foods. Daphnia, white worms, scuds, bloodworms, and mosquito larvae are all good choices for live food. They also appreciate eating live shrimp if you can find a clean culture source. For frozen food, you can also grab brine shrimp, mysis shrimp, beef heart, krill, and copepods mixes.

If you can get them to eat freeze-dried foods, you can add tubifex and blackworms to the mix as well. Though, on a whole, I would stick with frozen and live if you can. I have a complete shopping list below for you if you don’t know where to find some of these things (though I couldn’t include frozen, you’ll likely need to go to a store for those.)

Betta macrostoma Diseases

Macrostomas don’t usually have a ton of illnesses. When they die, it’s usually from keeper error. However, the few issues that they do usually have are included below (and you can find corresponding medications in the water care section above.)

The big concerns are usually fungal. Because they live in such acidic environments, they don’t usually have to deal with fungus in the water. If their pH is brought up, the fungus has a chance to survive and the fish have little to no defense mechanisms for dealing with it so it can get out of control quickly.

Columnaris (Cotton Mouth Disease)

Fin Rot & Tail Rot

Costia

Macrostoma Tank Mates

I do not suggest this. If you want to keep macrostomas, I highly suggest you try to breed them. As long as there aren’t enough captive-bred macrostomas on the market, people will feel the need to buy them from the wild. If people are willing to buy from the wild, people will be willing to do illegal things to take from the wild. Since they’re so rare to find (and they’re threatened,) I strongly advise anyone who wants to keep macs to breed them. The best chances of breeding success will be with no other tankmates.

Hang on while I quickly step down from my horse.

But, if you’re going to make the choice to put them in a tank with other fish, I’ll at least help you make a decent choice. Macs are easily intimidated by large, boisterous fish and can be easily outcompeted for food. Most of the time, macrostomas don’t seem interested in eating non-shrimp tankmates, so you can keep them with some pretty small fish. But I would still be careful and watch for any potential predation.

So, with that in mind, you’re going to want to go for small fish with small mouths that are unable to eat any potential fry but aren’t easily intimidated by much larger fish, aren’t aggressive, can deal with soft water and lower temps but don’t need a ton of tannins or plant cover, and don’t mind some water movement.

This, if you didn’t already guess, is a pretty (and specific) big ask and I make no guarantees any of these will work because your tank setup may be unsuitable for the species.

Pencilfish (Nannostomus sp.)

Rasbora sarawkensis (No common name)

Breeding Macrostomas

Breeding macs is a dream project for most serious fish breeders (somewhere between a breeding colony of zebra plecos and pygmy chain loaches.) Getting macrostomas to breed once they’ve paired isn’t hard, and getting macrostomas to pair isn’t too difficult either. The difficult part is getting the male to hold the eggs for full-term.

You’re going to want to get a group to allow a pair to form naturally. Once a pair has formed, they’ll usually live together without any squabbling unless they feel like they have no space. Of course, to get a pair you’ll need a male and a female. Males are much rarer and harder to come by than females because only an estimated 10 – 15% of the fry will be males.

When not stressed, the coloration is a dead giveaway.

When the fish are stressed (such as right after shipping) or young, look to the dorsal fin to spot the eyespot on a male (or not on a female.) Even severely stressed or younger males will have a slight black outline.

The pair’s first spawn will likely be in the “pairing” tank, and you probably won’t see the spawn or the resulting fry. You may not even notice your male was holding eggs. If he gets stressed, he’ll swallow them. But once they’re pair (or look like they’re going to pair up) it’s probably safe to move them to a spawning tank.

Spawning

As with most betta species, the female usually initiates the spawning. If you’re familiar with betta spawning, you’ll see some familiar flaring, fin flashing, wiggling, and embracing here. If you’re not, the female will usually approach the male in a “wiggle.” If receptive, the male will usually respond to the female with his mouth open and fins out.

From there, they may flare a little, open their mouths at each other, and she might continue to wiggle at him (which looks like a suggestive body slap, if you’re familiar with cichlid aggression and spawning.) From there, they’ll usually orient themselves to wrap.

The male will wrap himself around the female and fertilize the eggs as they’re released. Both parents will work to pick up the eggs together and the female will spit the eggs she’s collected into the male’s mouth. Sometimes the male won’t take them, but she’ll hold onto them most of the time in these cases.

Egg & Fry Care

The male will hold the eggs in his mouth for anywhere from 14 – 35 days, although 14 being the average. Once they eggs have hatched and they’re free-swimming, he’ll spit out a cloud of fully-formed fry. Since they’re mouthbrooders, they have much smaller batches than other bubble nester betta species, usually, only 10 – 20 fry will emerge from 20 – 30 eggs.

The trickiest part is making sure macrostomas hold their eggs to full-term. Most males will swallow the eggs or spit them prematurely. In either case, the survival rate isn’t good (if survivable at all.) If your male has a track record of eating his eggs, you can always try stripping the eggs (also sometimes called “milking” with later stages of development) and artificially hatching them.

This person had success hatching artificially:

https://youtu.be/Ax0YLz1Li0E

Once the male spits out the fry, provided he does, they’ll be as large as 1/4″ and able to eat microworms, vinegar eels, and baby brine shrimp. Within three months they’ll be large enough to send to their future homes, though they’ll likely need some additional growth time before they’ll be ready to produce fry of their own.

Further Reading & Resources

IUCN – Brunei Beauty

IBC – Betta Species By Complex