When a male betta is healthy, he always builds a bubblenest in the hopes that a fertile female will soon swim by. It is the male who takes care of the baby fish (fry). He spits out a series of large bubbles that float on the surface of still water and then waits for a passing female.
Making a Nest
When an egg-laden female comes by, they do a rough courtship dance that looks like a milder version of fighting. Then, the male curves over the female in a horsehoe-shape. As the female releases her eggs, the male immediately fertilizes them. The female lays an average of 350 eggs, but usually not all of them will survive. The female will drift as if stunned, while the male places the fertilized eggs in each of the bubbles of the bubblenest. They can repeat all of this for up to one day.
Fry and Bubblenest
After both male and female betta place all of the eggs into the bubblenest, the male chases the female away. He replaces any dropped eggs until they hatch in 2 or 3 days. He guards them for another four days and then the fry make their own way in the world.