he either died natrually, and the other fish ate the body (. Or one of the irredescent sharks killed him , then ate him. Oh and by the way. Irredecent shraks grow VERY large, large than the adverage aquarium can hold, I've heard one needs like 500 gallons. It is this reason they should not be...
Omfg...don't know why people are saying bettas don't need a heater or a filter. Bettas are tropical thus they require temperatures from 78-80F. If they don't have this temp. and are left at room temp. then after so long it lowers their immune system, and they end up getting sick, and dying :'(...