Male bettas will flare their gills, spread their fins and twist their bodies in a dance if interested in a female.
If the female is also interested she will darken in color and develop vertical lines known as breeding bars as a response.
Males build bubble nests of various sizes and thicknesses at the surface of the water.
Most tend to do this regularly even if there is no female present.

Plants or rocks that break the surface often form a base for bubble nests.
The act of spawning itself is called a "nuptial embrace", for the male wraps his body around the female; around 10–40 eggs are released during each embrace, until the female is exhausted of eggs.
The male, in his turn, releases milt into the water, and fertilization takes place externally.
During and after spawning, the male uses his mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the female sometimes assists her partner, but more often she simply devours all the eggs she manages to catch).
Once the female has released all of her eggs, she is chased away from the male's territory, as she will likely eat the eggs.

If she is not removed from the tank then she will most likely be killed by the male.

The eggs will remain in the male's care.
He carefully keeps them in his bubble nest, making sure none fall to the bottom, repairing the bubble nest as needed.
 Incubation lasts for 24–36 hours; newly hatched larvae remain in the nest for the next two to three days until their yolk sacs are fully absorbed.
Afterwards, the fry leave the nest and the free-swimming stage begins.
In this first period of their lives, B. splendens fry are totally dependent on their gills; the labyrinth organ which allows the species to breathe atmospheric oxygen typically develops at three to six weeks of age, depending on the general growth rate, which can be highly variable.
B. splendens can reach sexual maturity at an age as early as 4–5 months.
Male bettas will flare their gills, spread their fins and twist their bodies in a dance if interested in a female. If the female is also interested she will darken in color and develop vertical lines known as breeding bars as a response. Males build bubble nests of various sizes and thicknesses at the surface of the water. Most tend to do this regularly even if there is no female present.
Plants or rocks that break the surface often form a base for bubble nests. The act of spawning itself is called a "nuptial embrace", for the male wraps his body around the female; around 10–40 eggs are released during each embrace, until the female is exhausted of eggs. The male, in his turn, releases milt into the water, and fertilization takes place externally. During and after spawning, the male uses his mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the female sometimes assists her partner, but more often she simply devours all the eggs she manages to catch). Once the female has released all of her eggs, she is chased away from the male's territory, as she will likely eat the eggs.
If she is not removed from the tank then she will most likely be killed by the male.
The eggs will remain in the male's care. He carefully keeps them in his bubble nest, making sure none fall to the bottom, repairing the bubble nest as needed.  Incubation lasts for 24–36 hours; newly hatched larvae remain in the nest for the next two to three days until their yolk sacs are fully absorbed. Afterwards, the fry leave the nest and the free-swimming stage begins. In this first period of their lives, B. splendens fry are totally dependent on their gills; the labyrinth organ which allows the species to breathe atmospheric oxygen typically develops at three to six weeks of age, depending on the general growth rate, which can be highly variable. B. splendens can reach sexual maturity at an age as early as 4–5 months.
Siamese fighting fish