*sigh Depends on what they really are. Most killifish do fine in a ten. But golden-eared or golden-wonder killies may kill each in a tank that size. They get like 5" and are mean to each other. I think they mostly eat insect larva in the wild (do great on bloodworms) but they will eat newborn fry that fit in the mouth. Try the AKA site
http://www.aka.org/aka/modules/content/?id=2 and try to find out what they are.
Is this them?
http://aqualandpetsplus.com/Minnows,...n%20Wonder.htm