Based on the position of the humeral spot the two species that jump to mind are C. alta and C. anthurus but neither comes from the area where you're collecting fish. Near Manaus, correct? I'll have to do a little more research. The other problem is they are very young fish. They may need to do some growing and develop some of the other identifying traits.
EDIT: LOL I also responded to your post on The Cichlid Room Companion. Now that I have a better idea of where the fish were collected I can make some better guesses!!