i have a pair in a 29g i havent seen them harm anyone at all , they are slow movers so they wil ge picked on by faster more aggressive fish. They are with a rosy barbs and bristlenose plecos and an angel fish and i havent seen them even remotly be agressive. I dont know how to sex them though i tried going by point and less pointy fins and one of mine is brightr in color. They are imo peaceful.