The male will build a bubble nest. Bubble nests can be large or small; covering the entire top of the aquarium or not much larger than a grapefruit. If something is floating on the water, like a leaf, the male will usually build his bubble nest under it.
You can prompt a reluctant male to build a bubblenest simply by floating a plant on the surface. Many breeders use plastic lids (thoroughly cleaned, of course) to float on the water. Anything can be used, so long as it floats, though research suggests that round items that are yellow and about the size of a grapefruit work best. This may be because they look a bit like the large floating leaves of the bettas wild environment.
When to put the male and female together
The male will flirt with the female in between working on the bubble nest. He will flare, swish his tail and bend his body back and forth.
When the female is ready she will have dark vertical bands on the side of her body, and will position herself so that male can see the bands.
Once the fish are together, there may be quite a bit of aggressiveness on the part of the male, or the female, or both. They will nip at each other, and the female may decide to retreat. It’s a good idea to give her a place to hide every once and awhile. Sometimes a male will be so aggressive, that he will kill his prospective mate. Keep an eye on your pair to make sure they are not mismatched at this critical time.
After anywhere from a few rounds of this to a few days later, a receptive female will eventually follow the male under the bubble nest, where the actual spawning will happen.
