I usually keep one in an aquarium. I kept two females in a larger aquarium, but they didn't interact much with each other. It was more like, "This is my territory, stay away!"
Once I had about 25 (twenty-five) in a 180-litre aquarium, males and females, and that worked well for a while until I gave them away. I suspect that in their natural habitat during the dry season, they stay together in large numbers in the last remaining pools and are not aggressive in this crowded situation, and why should they be? This is also known from other species.
When there is more space available during the rainy season, they want to reproduce and fight for their territory. With two males in a 200-litre aquarium, usually only one will remain in the long run.