Will your jack dempsey try to eat your bala shark?

yep your 10 inch jd is going to eat your 15inch bala shark... think about that for a min. not to be rude but research the fish your planning on buying. A jd might eat a baby bala but a goldfish would eat a baby bala, a goldfish would eat a baby jd to. Fish eat smaller fish no matter what the species is. All in all a fullgrown jd and a full grown bala would be fine together.