One of my bettas will only eat if he is in a smaller jar. I have three tanks/ vases that each hold about a gallon of water a piece and one of my bettas stops eating when he is kept in his. For awhile he was kept in a 1 quart mason jar and he will only eat now when he is in his mason jar. He doesnt seem to mind the confined space and his water gets change atleast everyother day. Does anyone know why this might have happened?
There are pics of him in his Jar below:



