When i bought him..he was beautiful...4 months later when i put him in the "right" size tank from being in a bowl he went bannanas..i sure hope he stops..i think maybe they like short tails...btw...your betta is beautiful..but im done with long tail bettas..i have another betta (avatar) he is not a bitter luckily..but if i ever get nother betta it will be a plakat...i get too sad with tailbitters :|
Some betta fish need to be gradually introduced to a larger home. It is much like taking a person from a third world country and plopping them in the middle of New York City; it's shock and stressful to some, immediate adjustment for others. How many hiding places do you have for him? How bright are the lights? More places to hide will reduce stress and lights that are too bright can cause stress.