The Siamese fighter is not difficult to breed. While the way I do it may not be the "the" way to do things properly but it is the way that works well for my purpose: having a large collection of colourful Betta splendens.
To breed these fish you will need to get fish of both genders. Always select the most colourful, active and well proportioned male. The colour of the male is entirely up to you. The female must be fat, colourful, active and also look good with a proper back shape. Again the colour is totally up to you.
To go about breeding the fish you will need a 45 cm tank with hood. Fill this tank about half way (a depth of about 10 cm) with neutral water that isn't too hard. Add some plants to the tank. Introduce the male Betta and feed him well. Condition the female separately and introduce her to the male by floating her in the male's tank in a glass jar. The male will at first be very upset by her presence but will over time warm to her an her to him. After a few days let the female loose into the male's tank. By now he should of started bubble nest construction. Letting the female go in the evening is a good idea, especially if the next day is Saturday or Sunday. You will need to observe the pair during and after spawning.
The pair will spawn without too much fuss at temperatures over 27°C. The male will collect the eggs (and sometimes the female will too) and spit them into the bubble nest. The spawning ritual will continue for some time until the female is emptied of eggs. Once spawning is complete the male will chase the female from the vicinity of the nest. You will now need to remove the female.
Some times the male will do a lousy job at egg/fry care. He just lacks practice. The female will be ready to spawn in three days. If the male stuffs up spawn them again. As they get to know each other they will spawn better and better. Some virgin males can't even get the positions right and as consequence you end up with infertile eggs. If problems persist rescue the eggs but scooping the nest/egg mass from the tank and incubate the eggs in a shallow tray floating in the male's tank.
Normally the male will get it right after a few tries. After 48 hours the eggs have hatched and 2 days later the fry are free swimming. The male will not molest the fry but it is a good idea removing him by the 7th day. While the fry are small he can do a clean up operation and eat uneaten food.
The fry should be fed infusoria at first but many of the fry will be able to take baby brine shrimp from becoming free swimming. Infusoria can be easily cultured by taking a large jar, putting some crushed lettuce of banana peels into it and adding boiling water. Once this has cooled add some tank water or sprigs of Java moss to add the infusoria starter. Leave this mixture in the light. After a few days the jar will be seen to be filled with a writhing mass of microscopic organisms. To feed, pour portions of this mixture into the fry tank. You will need several cultures. Refill the used cultures with dechlorinated water.
As the fry grow increase the depth of the water and begin water changes. It is important to use water of the same temperature or else you may damage the fry. The fry grow fast and if given enough space will be of spawning size in 3 months. Males should be removed from the shoal and grown up in isolation to get the best formed fins and fish. Large jars work well for this. Keeping the jars on top of heated tanks will ensure a constant warm temperature. Water changes will need to be done every day on the jars.
Excess males of high quality can be sold to pet stores. Sub standard males should be culled or put out to pasture.
Communities of multiple males and females can be established by NOT removing the males as they mature but keeping them together in the same tank. Raised together the fish will not normally develop their sociopathic tendencies.
It is best to get a new male or female for future breeding but F1 crosses can yield many interesting looking fish as regards colour.