let me add that they do need to eat. bettas are such a beginner fish, they too often people seem to get the idea they don't need to eat. however, they only need a VERY small amount of food. buy a thing of betta food and follow the directions on the can. it's only a few little sand grain sized pieces a day. also, you can keep other fish with him (assuming the tank is big enough for other fish, which a 15g certainly is). again, this is another thing most people who have a betta don't seem to know. you just can't put him in with another male betta, he'll get along with all other types, assuming the other types don't start the fight.