Originally posted by buckner
If I may ask, what's a bubble nest used for? Is there a specific reason they make them?
Male bettas make bubblenests for breeding (when the female lays eggs, the eggs are placed in the bubbles.) It is thought to be a "claiming territory" behavior as well, and is generally done by healthier fish who feel well enough to follow those instincts, however that is not ALWAYS the case, as I saw a quite ill betta (with fungus infection and probable swim bladder disease) in a cup struggling to work on a bubblenest at a pet store. My guess is the instinctual drive is just stronger in some than others.

Conversely, a betta can be in perfect health and not show much inclination to bubblenest. I notice mine in particular nest any time any change is made to their environment, i.e. water changes, plants/gravel moved around, etc. I believe they see a change in the territory and feel the need to reclaim it.

I think it is a good sign, the same way as a healthy appetite is, but I don't think it should be use as the sole gauge to how the fish is doing. I've seen people get worried and upset when their pampered betta doesn't nest when he is otherwise doing wonderfully. Some people might also see a betta in a tiny cup of water bubblenesting and decide they are perfectly happy in such dismal living quarters.