Why do betta fish fight?

[okiemavis]

Sorry, you are right about using gills to breath as well. However, I was under the impression that they do rely on atmospheric air, and that they can actually drown if not given access to air.

[iamntbatman]

You are definitely right about that. Since bettas usually prefer water with very little movement, there is usually poor aeration and thus fairly low amounts of dissolved oxygen in their water. Thus, bettas require access to the surface in most tanks.