I used to keep lots of them in tiny jars with plants - but it was a chore maintaining a bunch of unsightly algae-coated bowls with murky water.
Now, I only have two of those ugly things.
In a previous fit of impulsiveness common amongst serial hobbyist, I once ordered 8 (Eight!) mini-aquaria, each measuring about 10 inches cubed. At present, most of them are empty souls. Two of them, however, are in my room, and one is home to my happy fighting fish. Quite an industrious one - he's always tending to his bubble nest. Male betta's make nests with their own saliva, in preparation for rearing a brood of baby fighting fish.
My Betta's bubble nest. He keeps really busy fixing up his nest. Must find him a mate!
... and a wider shot. You can see the little fella on the lower right hand corner of this picture.
I like care-free systems - these aquaria do not have external lights nor aerators. I just make use of ambient light from a nearby window as a lighting source. For oxygen, I make use of live plants. I used to keep submerged plants in such set-up - but since I moved them to a location with lower lighting conditions, pretty much everything just melted.
Good thing I was able to cultivate this hardy Monstera plant, which is pretty much indestructible. I am more successful if I treated the aquarium as one watery pot. I did not have much success growing plants under water, and it was far easier to grow plants that grew above the surface.
This other fella is in a big goblet. It might seem cruel to keep him in what seems to be a tiny living space, but I rescued him from the pet shop where he was given only an inch of water in a disposable plastic cup. I think his present home is so much better. It has a sand substrate and a thriving Scindapsus plant. This bowl gets water changes weekly, and he's a perky fellow. Always bugging me for food.
Betta in a Goblet
I've managed to breed some of these beauties in a small 10-gallon aquarium previously. I had a fighting fish family, with one patriarch and a number of juveniles co-existing in harmony. I've read that this is possible if the spawn came from one blood line. I am still on the look-out for Betta females to keep these guys company - but first, I need to find a suitable home for them to raise their little dragons.
For now, they're bachelors living in condo's. Quite a good life, actually, compared to their previous existence in plastic cups in a pet shop.