I have kept and bred Bettas for quite some time. Many Betta keepers have asked me over and over on the correct way to do this for a successful spawn. These instructions should provide you with enough information to accomplish just that. Happy Betta Breeding!
The Breeding Pair:
make sure that the male and female are relatively the same size. Females are usually somewhat smaller than the males, but do not try to breed a very young male/female with a much older mate. Someone will get hurt.
Condition the Pair:
feed well, preferably live food (brine shrimp) and keep their water very clean. Allow the two to see each other for a couple of days and then remove the female from the male's site before placing him in the breeding tank.
small tank (I use 5 l/2 gallon) with approximately no more than 4-5 inches of "conditioned" water; a corner sponge filter; submersible heater set at 80; a plastic lid or piece of Styrofoam cup cut for the bubblenest; and plastic or live plants so the female can hide when needed. Do not have any rocks or substrate in this tank. Put the male in first. Let him get used to his surroundings for about an hour or so. Then introduce the female by putting her in a hurricane globe so the male can't get to her right away. They should show some interest in one another, and he should flare at her and start working on the bubble nest. (I had the experience a couple of times that the female was already full of eggs and very shortly after introducing her into the globe and seeing the male, she started to release her eggs very quickly. She had been bred several times before with the same mate. I released her immediately and the spawn began.)
When the bubblenest is fair size, and she displays vertical stripes and stands "on her head" in the globe, you release her. Also look for her "breeding tube" to be protruding. It is visible behind the pelvic fin. There can and will probably be some nipping and chasing during this time. As long as they are not sparing too badly, leave them alone. If one or the other is being torn up very much, they are not ready. Put her back in the globe. Some sparring will occur as this is the ritual of their mating but should not be permitted to last for great length of time. The process of the pair "being ready" can take from l hour to 4 or 5 days.
When they are ready, he will "entice" her to the nest, and she will eventually follow. The mating process can take anywhere from 1 hour to 4 or 5 hours. He will "embrace" her, squeeze the eggs out, and the eggs will fall to the floor of the tank. She will look like he has killed her, being very still and motionless for a few seconds, like in a trance. He will "catch" or pick up the eggs from the floor of the tank and "blow" into the bubble nest. (I had one pair that the male would not have anything to do with the eggs, and the female was the one who picked up eggs and put into the nest.)
When the spawning is complete, she will swim away from the male and "hide". He usually won't bother her as he is busy picking up eggs that fall from the nest. When spawning is done, remove her immediately (taking care not to disturb the nest) as she may become interested in the "eggs" and start eating them. The eggs are white and are a little bigger than a grain of salt. You will probably need a magnifying glass to see them hanging from the bubble nest.
Raising the Fry:
After the spawn and removing the female, you need to treat both she and the breeding tank with Maroyx. This prevents infection to her from any torn fins, and is needed in the breeding tank to keep fungus from developing in the eggs. You also need to cover the tank with plastic wrap or glass so that no "cooler" air is at the surface of the tank. When the fries' labyrinth starts to develop (at about 5 to 7 weeks), and they come to the surface for air, they can get pneumonia and die from the cooler air. I leave the cover on the tank for the duration, until they are moved to jars or taken to the pet store for selling.
Start an infursoria culture with lettuce and water or have on hand "microfood" to have something to feed the fry when they are ready. At first the fry will "live" off the yolk sac and do not need any food. Start to feed about 2 days after they hatch or when they become free swimming.
In about two weeks, you will need to start feeding either live bbs (you can set up your own hatchery) or microworms (which are started from a culture and not ordinarily found in petstores) to feed the fry. The microworms are easier to keep as the live bbs shrimp only last about 5 days after hatching. You need to keep two hatcheries going so there is a constant supply of food for them. They will need to be fed about every 4 hours or so, small portions at a time.
At about 36 hours after the spawn, you will notice little "black dots" with tails falling out of the nest to the bottom of the tank. The male will studiously go to the bottom of the nest, retrieve the "fry" and "blow" them back into the nest. When the fry become a little more free swimming in the horizontal position, you can remove the male from the tank. It is also possible to remove him earlier if he is not a good caretaker, eating the fry. This is where you really need to pay attention as to how many fry you have as he will be a good poppa at first, and the next minute eating every one he picks up. If you must remove him, the fry will land on the bottom of the tank and be okay there until they become free swimming.
You need to keep their water clean during the time they are growing up. Use
a very small plastic tube attached to air tubing or a turkey baster to suck
up the debris from the bottom of the tank. Run the water into something
clear so that you can look for and retrieve any fry that may have gotten
sucked up the siphon. Catch with white plastic spoon (so you can see them)
and replace back in the tank. Water replacement "has" to be the same temp so
as not to "chill" the fry and be conditioned to remove chlorine and
Betta fry are very, very tiny when hatched, and are very slow growing. Even after almost 3 months, they are still very little. It takes approximately 30 weeks for them to develop any color or have any size to them. They are usually not very active and most will basically sit on the bottom of the tank until feeding time. As they grow, you must pay close attention to them. As the males get older, you will notice them becoming aggressive with each other. This is when the males will need to be removed from the tank and "jarred". And this is where even more work will be involved. You need to have on hand many mason jars for the males, and these will all need to be cleaned on a regular basis. (I have had at times over 50 mason jars sitting around my house with these little fish in them.) The females will be okay together. As time progresses and the fry become larger, you can add water to the tank to bring it up gradually to being full. If there are quite a few female fry, they may need to be moved to a larger tank so as to not overcrowd them.
You may notice that after removing the male from the spawning tank, he
"acts" weird. He may be very tired from protecting and retrieving the fry or
even be "depressed" because his work is finished. Feed him well, add
"aquarium" salt to his water (l teaspoon per l gallon of water) and in a few
days, he should be back on track.
You may also notice after a pair has spawned, that very shortly they are ready to go at it again. If you have the room and proper setup, you can repeat the spawning, however, you should wait at least 2 weeks if possible so as not to wear the pair out. If you have your hands full with the spawn you already have, don't worry about breeding again. She may release her "unfertilized" eggs and he may build bubble nests, but neither of these activities will hurt them.
I think that just about covers the process of breeding these fish. Sometimes, you can just put the two together and immediately have a spawn, but don't hold your breath. My first spawn took several days, happened while I was away and was not quite sure there had been a spawn until I saw the fry falling from the nest. I was fortunate enough, however, to catch them during the act one afternoon and have the whole beautiful process on tape. Mother Nature works hard on making us look like fools, you know. But my son got an A+ on a report he did for his 8th grade Science class!!!