'Flaring' is a term used when betta fish lift up their gills on the sides of their heads as a fighting tactic.They do this to look bigger and more intimidating to their opponent. When betta fight with other fish, they get an adrenalin rush and this releases endorphins in their brains which is a healthy stimulant.
Since my Fighter Fish lives on his own in his tank, he doesn't get much real-life fish stimulation. I have read that it is healthy to 'fight' betta fish to get their adrenalin rush going. People normally do this by placing two male fighter fish in a tank and separating them with a piece of glass so that they can 'flare' at each other through the glass and not actually hurt each other.
Because this is healthy, I tried to use a mirror to entice Blue into a fight with himself. For a week, every time he saw himself in the mirror he would dart off on the opposite direction - obviously not a very brave fish. In any case, I continued to try with the mirror.
I could see he was tempted when he saw himself. He would stop and stare for a while in the mirror and then dart off. Each day I think he was getting a little more courage, until he finally did it!
I do still think that he is a naturally shy betta fish because I've seen other student's experimental betta fish and they seem to be far more active than mine. But as I said; I don't believe it is because of any illness, I just think that me betta is more introverted. I don't know if you can say fish have personalities, but I don't see why not.