Well, start to feed them both good quality betta fish food. Just as in nature, no animal in its right mind is going to be reproducing when food is scarce and if they have poor body condition, no female betta fish will product eggs (spawn) if she's not given the best in the food area. You could even try feeding them some tubifex worms (live wrigglers). With this diet regime (do not overfeed - it will foul up the water, once or twice a day is plenty) you will start to notice that :
* the male betta fish will start to build a bubble nest - some tend to do this anyway.
* the female betta fish will start to look decidedly plumper and with some paler colored varieties, you can even see the eggs inside her belly.
When 1. and 2. are present, you need to set aside at least an hour to supervise the breeding activities. This isn't a 'I'll just put them together' and then leave them for a few hours to come back to it type thing. It also isn't a 'sure thing' ie if I put them together, they'll do their thing and we'll have babies swimming out of our ears...Bit more complex than that I'm afraid.
# What can I expect when breeding my betta fish?
* expect the female betta fish to get a bit battered and bruised - which is why you need to be vigilant (similar to Syrian hamster breeding) and fish her out if she doesn't like his aggression and doesn't approve of his 'amorous' advances. Give her a few days to recover and try again.
* if they are ready for each other, you will notice what's commonly called 'the embrace' where the male betta fish wraps his body around the female and appears to be 'hugging the eggs out of her' - as she spawns, he releases his sperm to fertilize them. Then he will start his daddy duty (just like the penguins I must add) and care for the young. As soon as he has released her and is busy scooping up eggs with his mouth and popping them into his bubble nest, scoop the female betta out of the tank - that's it for her really.
* 3. in the next 2 days, the male betta will be tending to the brood and scooping whatever eggs fall out of the bubble nest and returning them to the surface again. Quite fascinating to watch really!
# The baby betta fish are here!
After about 2 days, you will notice little small fry emerging in the bubble nest. They need to stay in that nest for 36 hours as their gills aren't fully developed yet. Daddy betta fish will continue his job of scooping up young that start to sink to the bottom and bringing them to the surface. 2 days after they hatch or when you see the fry start to swim independently (usually about 2 days after hatching) - REMOVE the male betta fish or he may just decide to devour the whole brood...
# Caring for baby betta fish
If you're like any parent I know, you will realize that this is the hardest part in the breeding cycle. Some betta breeders have sworn that no matter what they've done, they're never as successful with breeding bettas in a tank environment as in a pond situation. I think it's to do with the normal pond flora and ponds not being exactly 'squeaky clean' - baby betta fish have tiny mouths and they need to feed on small protozoa and other small microscopic little beasties living naturally in your pond water. Aquariums tend to run out of this pretty rapidly.
* You can breed the stuff by taking a large jar (shallow and wide rimmed to allow plenty of oxygen), fill it with some tank water, putting some grass or straw (straw is probably better because you can never be sure if someone's sprayed pesticide on the lawn) in the jar and then leave on a sunny window and just watch the water come alive with all sorts of creepy crawlies (yummy food for your baby betta) - this will probably take about 3-4days. If it starts to smell too much, you've probably overdone the organic matter. Harvest an ounce or two from the top, be careful to avoid getting too much of the slimy stuff and then put it straight into the tank with the baby betta fish.
* After about 2 weeks or so, your baby bettas can move on to other stuff like finely crushed flake food - and I mean finely crushed. Baby bettas don't need a huge amount of flake food. A tiny pinch (and I mean tiny) of crushed flake food daily would suffice. By about 7 weeks your baby bettas would've reached 1 inch in size. It has been recommended that as soon as the baby betta fish reach about one halve inch that you separate each of them into individual small jars. As they begin to mature, you should be able to tell the males and the females apart.