Hi my tank has been going for about 5 days now, I have 2 zebra danios and 2 marble mollies. I've noticed that the bigger of each species seems to chase around the smaller of that same species, and the smaller swims away quickly and tries to stay away for awhile. The smaller danio and molly both seems to be fine, they don't look sickly or anything. So do fish just bully each other? They only bother the fish of their same species, the molly doesnt bother the danio, and vice versa.