Do Koi and Mollie's not "get along"? My housemate has a small 10 gallon freshwater tank, and we recently added two guppies, a sucker fish, and a koi to a tank containing a molly and rainbow shark(?). Yes, I know you shouldn't put a koi in such a small tank (plus there are temperature conflicts), but I had no say in that one. My housemate couldn't be convinced otherwise. As soon as he put the koi in the tank, the white molly immediately started sucking/nibbling the backside of the koi. This has persisted for the last couple hours. Is this normal behavior? Do we need to separate them in order for both to survive? Thanks for the help!