How come the blue male Betta fish gets fat?

Bettas are by nature round in the body. It eh fish is kept in a small container it will however probably suffer through lack of swim space. The basic rules for successfull fish keeping are. :- 1 inch of fish needs a minimum of 1 gallon of water. (A Betta is at least a 3" fish so it needs a minimum of 3 gallons of water. 10 gallons is better.) :- Every tank needs a permananently running cycled filter. :- Every tank needs at least 50% of its water replaced every week. Keepyour water at the right temperature and follow the above rules and your fish stand a reasonable chance of survival. Fail in any of them and I can guarantee that your fish will have constant health problems.