Bettas are found in swamps, rice growing areas, floodzone ponds, etc. They have a slow water adaptation - the labyrinth organ - to deal with low oxygen levels. But even in the Betta family, there are mouthbrooders from moving waters. Several gouramis, also with labyrinths, occupy similar niches. In Africa, the 'deadwater' niche is occupied by annual killifish, as it is in South America, with Rivulus and annual killies.
Labyrinth fish are popular in aquariums all out of proportion to how common they are in nature, because they tolerate rough conditions.
I caught some gouramis in Gabon out of water that was really moving. No aquarium could be that fast without serious turbulence in the corners and ends. I caught 2 different species in one quick stream. Nature breaks all our rules, but overall, water moves.
Fancy Bettas in nature would be like pugs in a wolfpack - their habitat is jars on fishfarms.
A good exercise is to leave the cities where most of us live in mid summer and take a few walks out in nature. Look at the water and compare it to your tanks. How many still as glass water bodies do you see, compared to ones with waves, currents, riffles or wind driven turnover?
