And give it a few more days, they ll start taking chunks out of each other s fins. That is when the breeder steps in and jars the bullies. Soon, all males have to be jarred and only females will be left together. Variations in aggressive behavior. Some strain are noticeably more aggressive than others, and even the females are nasty to each other.
Some strains are more peaceful and can sometimes be kept in groups.
A breeder friend of mine was marveling at my large 60 gal community tank, housing about 40 adult bettas, mostly females but also three large males. These bettas were all from the same spawn and knew each other. This strain was a more gentle strain and it was a treat for the eye to see all these bright red and pink bettas swimming in harmony together. The pecking order. When kept in a community tank, bettas will establish a pecking order.