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B. Macrostoma - Breeding

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Ok... so you've gotten this far. Your Macs have settled in properly, you've gotten the water quality thing under controls and hopefully, the male is starting to show interest in the female. You can tell he is especially "in the mood" when he starts flaring and displaying for hours on end. Now you start thinking about what it takes for a successful spawn. Well.... you've certainly come to the right place.

But before we start, I have to make it clear that whatever I will say in this section is based solely from my personal experience and what worked for me. Because of the dearth of breeding information out there, I cannot say for sure that my way is the "best and only way", but i can definitely vouch for the effectiveness of the methods that i use. If you find a better way out there, then i say go for it! After all, there are others out there who have developed their own methods that work fine for them as well.


Well, to start with, you're gonna need at least a 20 gal tank. Some people have used smaller tanks, which is ok if you can keep the water quality up to standard. Otherwise, for the same reasons that I list in Housing (Tank Size), I wouldn't go with anything less than a 20gal. I have had great success with new pairs in standard AGA 29gal. For mated and established pairs, a 20 gal - Long (20L) works great.

Make sure you provide lots of hiding places for the male to hide after mating. You will notice that the male will take his mouthful of eggs and hide away. Fill the tank with lots of driftwood, plants, oddly shaped rocks, slate caves or even PVC pipes.

Here's a 29gal with lots of hiding spots. The male is nowhere to be seen (good news). Note the breeding net used to separate the fry when they are released.

betta macrostoma breeding tank

Recently, i've begun to house pairs permanently in their own 20L or 29 gal tank. Instead of removing the parents after the release, I remove the fry. But in order to do this, there needs to be a divider in the tank. The female lives permanently on one side, and the male lives permanently on the other. They only come together to mate. It is important to keep the pair separated in between spawns. Otherwise the male, after releasing the fry (and starving for a month), might immediately go and mate with the female. If so, he will have to spend another month starving. Weakened by 2 months of starvation, the male sometimes do not survive.

Other people have opted to use a bare bottomed tank with minimal hiding spots for spawning, but I find that the parents are not as nervous if there are more hiding spots. I like to keep lots of plants in there because it helps to suck up the nutrients. This is especially important when you start feeding the fry multiple times daily (see "raising fry" below) .

Here's my 20L with the divider. In this pic, the left side is normally the female's and the larger right side is the male's. Here you see the female in the right side and the male is no where to be seen. Here they have just mated and the male is hiding behind the wood. I will move the female back to her side before the male releases the fry.

20 gal betta macrostoma breeding tank

As for filtration, I prefer to use a HOB filter (aquaclear) with a pre-filter sponge. Just before the release (about week 3), I turn the filter flow down to a minimum so as to prevent fry from getting sucked into the filter or sponge.

I prefer to keep my breeding tanks relatively sparsely furnished or planted. Perhaps a clump or two of java fern and perhaps some anubias attached to a piece of wood. Pretty much anything that can be easily removed from the tank. This is to make it easier to hunt for and remove fry (they are surprising fast) after they have been released.

I don't do anything special to the water or temperature. Whatever water and temperature they have been living in, is whatever they will breed in. I have seen little evidence to suggest that any particular water condition triggers spawning. It just seems like once they start, the horny little things just keep going and going....

Some other things to have on hand for after the spawn include:

  • Brine Shrimp, Microworms or Walterworms
  • Brine Shrimp Net to scoop up fry in order to separate them
  • Breeding trap or Breeding net to hold fry after being separated
  • 2-1/2 gal tank to move the fry about 3 weeks after release.
  • 10 gal tank to move the fry after they start "begging" consistently.
  • Larger grow-out tanks for grow-outs until they are ready to be shipped. Generally a 40 breeder or two-20gal tanks for an average spawn.

More of the above will be discussed in the section on Raising Fry.

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It is very important that the pair be adequately conditioned before attempting to breed them. I have noticed that nice and chubby females tend to produce larger spawns. The largest spawn that i have had was 17 fry from my chubbiest and roundest female. Otherwise typical spawns tend to yield about 10 fry or less per spawn. I have also noticed in my B.Splendens that chubbier females tend to have larger and stronger young. At this time i have no reason to doubt that this is also the case with Macs.

Equally or perhaps even more importantly, we need to ensure that the MALE is adequately conditioned. Unconditioned females may lead to smaller spawns. An unconditioned male might possibly be weakened to a point that he might die. This is because males can spend up to a month holding eggs. During this time, he doesn't eat and hence needs to have enough fat reserves to last the entire holding time span.

It is important to make sure that while you are conditioning the male, that you keep him apart from the female by either a tank separator (available at your local big box pet store) or move him to a separate tank. I prefer the separator so that i don't have to remove him from familiar surroundings. If he has lived in the tank for a while, he would probably have his favorite caves and hidey holes already mapped out. Chances are that he will use these same hidey holes to hide out during the holding process. The reason for separation is that males are just downright horny. It is not uncommon for a male to mate with a female immediately after releasing his previous clutch of eggs. Already weakened from 3-4 weeks of fasting, if he is allowed to breed and thus go another 3-4 weeks without adequate energy reserves, it might just kill him.

NEVER try to breed a male that is thin, sick or not eating well. The month long hunger strike will almost certainly kill him.

For 2-3 weeks before the planned breeding, supplement his food with foods that are higher in fat content. If your mac is accustomed to commercially available foods, the nutritional information may be easily obtained from the side of the bottle or the packet. Live foods such as banana worms and grindal worms are high in fat and may also be used to supplement his regular foods. If you feed lean raw meat such as beef hearts, you may mix in some nicely marbled meats to up the fat content of his diet.

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Mating & Incubation Process

If you have bred B. Splendens then mac spawning is a piece of cake. For one, the male doesn't usually try to kill the female. In fact, it is actually quite romantic. No rough sex for this pair.

As with most Betta species, the male will court the female by displaying intensely. If you notice that the male is more "colored up" than usual, there is a high possibly that love is in the air.

Because they are mouth brooders, the male does not need to build a nest. During courtship, he fully extends all his fins and approaches the female while displaying his vibrant colors. His reds will take on a deep color and his blacks will be very prominent. Quite often, he will approach the female from her side and seem almost to "stiffen up" as he tries to spread his fins as wide as he can. His ventral (pectoral) fins seem to cross when viewed from the side (like someone crossing their legs in bed). Quite often he will open his mouth real wide, almost as if he is yelling at her. Fighting and chasing is uncommon, he's a real gentleman.

The female will generally turn her body such that she forces him to approach from the side and slightly forward. She too may flare her fins in reaction to him and may even open her mouth wide to scream back at him. The courting and display may actually go on for hours before actual mating will occur.

Here's a vid of me sneaking up on my teens and busting them trying to get fresh with each other through the screen divider. They see me and get embarassed.

Eventually they start swimming in circles close to the surface of the water as if chasing each other's tails, as if trying to get themselves into the mating position.The circle eventually gets real tight as they embrace to spawn. Simultaneously as the male arches his body to the side to try to embrace the female, she will roll over on her side or sometimes even on her back. Because of the size of adult macs, it is unlikely that he will fully embrace her as B. Splendens do. It's more like a loose embrace.

During the embrace, sperm and eggs will be released by the male and female respectively. The fertilized eggs will slowly sink to the bottom. Both parents will dive down and pick up the eggs in their mouths. The female then transfers any eggs that she has picked up to his mouth through a "french kiss". Then they go back to the surface, and repeat the embrace. I've never actually waited and watched the entire spawning process, but it's definitely more than an hour. Because i started to get bored and decided to leave the alone.

I have yet to actually capture the breeding process on camera. They seem to like to get it on when they are certain that there are no cameras around around. Perhaps they are shy.

One of my customers who had some of my macs actually managed to capture the mating process on camera. Check it out HERE (Will open another window).

When the female has given up all her eggs, she will stop going into the embrace with the male. However, for several hours, he will continue to follow her around the tank and even try to pick at her vent or attempt "french kiss" her mouth in an attempt to get her to surrender more eggs. But eventually her gets the picture and retreats to his hidey hole.

It is not necessary to remove the female immediately after spawning, but she should be removed prior to the release of the fry in order to prevent him from mating again.

For the next 3-4 weeks, don't be surprised if you never see the male. It can be quite freaky the first time round, constantly worrying that he might have died somewhere in the rocks or something. But if you have conditioned him correctly, and if he is healthy to begin with, then you shouldn't worry too much. In fact, if you see him after a week two, you can be sure that he has eaten the eggs and you have lost the clutch. So in fact, you actually want him to disappear for at least 3 weeks because he will only emerge if he has eaten the eggs or released the fry.

I got lucky this time... he male came out briefly for a photo shoot. Note the very obvious bulge under the chin.

betta macrostoma holding

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Raising Fry

1) Collecting Fry

If you noticed that your holding male has suddenly appeared after 3 weeks, first make sure that there are indeed fry in the tank. Go poking around the tank with a chopstick or something and look to see if any fry show up. Focus on heavily planted areas and at the sides of the tank just above the sand. Fry are small (but not that small). About 1/4" or so and are surprisingly fast swimmers. If you see any fry, and your tank is planted, then there are two ways to go about removing fry.

A) Tear up the entire tank looking for fry.

This would be the easiest and most sure way of getting all the fry. If you had set up the breeding tank with easily removable plants / wood / furnishings etc as suggested in "setup" (above), this wouldn't take too much effort. Just be careful when removing stuff, especially plants such as java moss which may entrap fry among its branches. You may want to take double precaution by placing the removed plants / furniture in a bucket of water (with the same chemistry as the main tank), just in case you accidentally remove some fry. You can scoop them up from the bucket if you did indeed pull some out by mistake.

Turn off any power filters and scan the bottom of the tank, focusing on the sides of the tank just above the sand. Have a small to medium net already in the tank and scoop them up as you find them (easier said than done... you'll see).

B) Leave the tank intact and scoop fry as you see them.

Now.. although this is significantly less destructive on the tank, but it may take several days to completely remove all the fry. Basically, you scoop out fry as you see them. But this also means that you may need to dose the tank with BBS for the first couple of days which in itself brings out a whole bunch of other problems with water quality. But somehow fry do manage to survive quite a long time in the main tank and it is not uncommon to find fry a couple of weeks after release. I have no idea how they do it, but perhaps they pick at leftovers from feeding the adults.

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2) Housing /Feeding Newborns

Now that you have managed to remove all (or at least MOST) of the fry from the main tank, you have another choice to make, that is to raise the brood in a separate tank or in a breeding trap within the same tank. I personally find that there is less mortality if you raise fry in a breeding trap within the same parent tank. This may be due to the fact that the fry are already accustomed to the water chemistry within the main tank, after all they were hatched in that very water. Besides that, the larger volume of water in the main tank promotes more stability in terms of water chemistry. So i'm going to encourage the "same tank" method.

Here's a pic of a 2 week old fry. Compare his size to to the java moss:
betta macrostoma fry

There are two kinds of breeding traps that I have used with success. The key however is that the trap MUST have a flat bottom without holes. This is so as not to allow BBS or microworms to slip through the holes before the fry get to them. Newborn Mac fry are not the most voracious eaters in the world and really take their time to eat. A flat bottom that will hold squirming microworms and BBS will help keep the food around for longer before they eventually float away.

The first kinds of breeding traps are the clear acrylic floating breeding traps with a flat (non perforated) bottom. The vents for these traps are usually on the side of the traps. It is important to make sure that the slits are small enough not to allow fry to swim through but may allow poop and uneaten foods to eventually flow up.

The second kind is the "netting" type breeding traps which is stretched over a scaffold. These require a little bit of work to make it safe for fry. Firstly you need to create a flat bottom for the netting to prevent food from freely flowing through. I use a piece of 1/8" plexiglas cut to fit the bottom of the scaffold. It is also important to place the plexiglas between the scaffold and the netting (as opposed to right above the scaffold). This is because it may trap adventurous fry between the plexiglas and the netting, requiring frequent liberation of these wayward fry.

Here's a pic of fry in a net type breeding trap. This pic was taken before I figured out that I needed a piece of plexiglas at the bottom to keep the BBS from simply falling though the mesh and disappearing.

betta macrostoma fry

Feeding is relatively simple. Squirt either instar 1 (freshly hatched) baby brine shrimp or microworms into the breeding trap. As long as there is something (like a flat floor) to prevent the live food from floating away, the fish will eventually get to it. Feed enough to see bulging orange bellies (white if microworms). And then squirt away the excess so that they don't overeat. Depending on your schedule, you may have to feed them up to 4-6 times a day. I notice that the more frequently they are fed while keeping up good water quality, the faster they seem to grow.

After about 2-3 weeks in the breeding trap and everyone is healthy and eating well, then it is time to move them to their own tank and prepare them for transition for dry foods.

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3) Juveniles

I find that the best way to transition fry onto dry foods is to do it in a relatively small bare bottom tank. The main reason being that with a smaller tank, you can add a small amount of fry foods in suspension as opposed to adding much more to be able get the same density of food in the suspension. BUT it is extreme important to do frequent water changes to remove uneaten foods which can foul such a small amount of water very quickly. There should be daily (twice daily even better) siphoning of fry tanks with a rigid airline to suck all the gunk from the bottom of the tank. Once all the fry are eating dry food readily, you can move them to a larger tank.

Here's a pic of my fry in a 2-1/2 gal tank just after graduating from the breeding trap. Furnishings consist of a clump of java moss and and airstone. Daily siphoning of bottom and 50-70% water changes.

betta macrostoma fry


Here's a vid of the same 2-1/2 gal tank a week or so after. They are beginning to show their stripes even at such a young age. Comparison with each strand of java moss will give an indication of their size at this point. Tank bottom is still clean!


Generally in smaller tanks, I have no problems transitioning juvies straight from BBS / microworms to crushed flake or crushed granules. I like to use Tetra granules. They can be easily ground into a fine dust. I add water to the crushed powder and agitate it into a suspension, which I then feed to the fry. They probably won't eat it first time round, but don't give up... they'll eventually get it right. Here are some tips that might help

  • Always transition slowly. Don't just suddenly stop feeding their old foods and start their new. Always make sure there's an overlap so that in case they refuse to eat the new stuff, they won't starve to death.
  • Try feeding the new foods before adding the old stuff. Squirt some of the suspension into their faces and swish around. Wait a little while and observe them for a while to see if they actually eat. After waiting a while, then go ahead and feed their usual bbs or microworms.
  • As they start eating the dry stuff, slowly increase the amount of dry stuff while slowly decreasing the live stuff.
  • Fish are most hungry in the morning. You'll normally get good results at the first feeding of the day.

Once they are eating the suspension well, they you can try transitioning to crushed dry stuff (without suspension) using the same principles listed above.

As soon as they have made the transition to dry foods, the hard work is done. Now its a matter of keeping up your feeding and water change routine.

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4) Culling / Inbreeding

Oh yes.... a subject that is unpleasant but needs to be addressed. Every experienced B. Splendens breeder knows the importance of keeping undesirable traits out of their breeding lines. Much inbreeding and bad selective breeding has caused many problems with many Splendens lines. Traits such as curved / bent spines, red wash, uneven ventrals, uneven DT lobes are traits that should be eliminated but unfortunately are allowed to survive through irresponsible breeding practices and repeated inbreeding.

It is important not to allow B. Macrostoma to go down the same path as B. Splendens. Fish with deformities, must be culled so as not to allow those traits to continue. Because most captive Mac lines are still pretty close to F0, there is still much genetic variability. Hence many times you'll notice that some pairs produce fry that are a hodge podge of shapes, sizes, finnage etc. It is responsible breeding technique to select for the best genes and cull those that are very obviously bad traits.

In order to maintain a good genetic diversity, it is good practice to breed with individuals outside their lines. This ensures the longevity and strength of this beautiful fish.

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5) Growouts

If you have been keeping up with feeding and water changes, your macs should be growing fast and are still bottomless eating monsters. Unsexed juveniles are ready to be shipped when they are about 1-1/2 inches. But if you are raising them to select for breeding stock or to sell them as pairs, then you're gonna have to raise them till adulthood. This generally means that you'll have to start separating them when they get to a certain size or when individuals start showing aggression.

Generally, in a centralized filtration system, males are separated and placed in 5 gal tanks (or if you can afford the space 10 gal tanks). Females may be allowed to remain in the community tank if they are civil. Sometimes certain females may show unusual aggression and may have to be separated like the males.

Happy and hungry youngsters in a 10 gal growout tank.

betta macrostoma fry

Now you are beginning to realize what a huge space requirement is needed to raise macs to adulthood. Imagine the jarring space needed to raise a brood of B. Splendens... now imagine each of those jars were 5 - 10 gal tanks. This is the main reason why juvies are sold as unsexed pairs except for a select few.

Well.. that pretty much covers raising fry. Macs are not terribly difficult fry to raise. They are generally hardy and tolerant of changes and will do well with breeders with average breeding experience.

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On the urging of my friends, I started this website by putting together the original (and quite successful) B. Macrostoma pages. Since then it has grown to include much more aquarium related information. All this time I've provided all this info and lots of free e-mail support to anyone who needed help. The advertising on this page helps out a little to offset the cost of webhosting. So if you see something that you may be interested in listed within the GoogleAds banners, then please don't hesitate to check it out.
I thank you all for your great interest in my articles and I hope to keep hearing from you guys, even if it is just dropping me a note to say hi. God Bless!

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