Betta fish are teritorial, this is why they fight. Most often the agression and fights occur between two male Bettas, however a new female introduced into a tank can threaten the existing male's dominate role and cause him to attack, so care must be taken when introducing Bettas.
Taking the Mystery Out of Betta Breeding
A good way to get a male and female together for breeding is to start with them in separate tanks that are side by side, or in the same tank with a tank-divider in place to keep them apart, just so they can see and become familiar with one another before being able to interact physically. It will take between 3 and 5 days before they're ready to be allowed to interact, and even still a close eye needs to be kept on them at first to ensure the male doesn't feel threatened and attack.
The best time for breeding is when your Bettas are between 6 and 12 months of age. Your male should be larger than your female, and the more energy and vibrant colors your fish have the better. These are signs of healthy fish.
The bottom of your breeding tank should be bare, and the water level kept at about 5 inches deep. Your water should also have a pH level of 7.0 and be constantly kept at just about 80 degrees fahrenheit. These are the most optimal conditions for breeding, and normal healthy living for your Betta fish.
When the male is ready to breed, he will begin making a bubble nest on the surface of the water by blowing tons of tiny bubbles together. You can aid him by making sure there is a large leaf floating in the tank for his bubble nest to stick to and build out from. It can take several days for him to complete his nest.
Even though the tank bottom should be bare, you will want to ensure there is some vegetation or tank decoration available where the female can hide. Male Bettas can get very aggressive during the courtship phase, so the female needs available shelter if he becomes too rough. She'll also need a place to hide out after she's laid her eggs. The male Betta will handle all the caring chores for the fertilized eggs.
Once the bubble nest is complete, and the courtship has led to the male impressing the female to stimulate her into laying eggs (up to 500), the female will usually turn over (belly up) and the male will wrap himself around her as she lays the eggs. Fertilized eggs will sink to the bottom which is why having it bare will help the male at this point, because once the female finishes she will retreat to shelter and the male will begin scooping the fertilized eggs from the bottom into his mouth, and placing them on the bubble nest.
It is a good idea to remove the female from the breeding tank at this point if you can without disturbing the bubble nest. Being a devoted father, the male Betta can view the female as a threat to the eggs in the nest and attack her. Also, you will want to discontinue changing out water in the breeding tank until after the baby fish are 2 weeks old. For this reason you need to be extra careful not to overfeed the tank in order to prevent the water from clouding too much.
The eggs will hatch within a few days into fry, which wil hang down from the bubble nest for several days as the fry feed from the yolk sack. In about 3 to 4 days the fry will begin swimming around freely, and at this point you must remove the male Betta (their father) from the tank or he will turn on his young and eat them.
At this point you should begin feeding the fry twice per day, either Baby Brine Shrimp or a special baby fish food called Daphnia. Tetra can also be given to the fry, but some think it is not the best starter food for Betta fish. Just remember not to overfeed the tank or your water will cloud up quickly and place the young fish at risk.
Once the fry are two weeks old you can begin changing out the water in the breeding tank again, but be very careful as the baby Bettas will still be small and fragile.
If all has gone right, you should have a tank full of young Bettas to either separate into multiple tanks for yourself, or to separate and sell to local pet stores, or to just give to your friends and family.