I'm 20 years late but I came across this in my digging for ways to diagnose the two species against eachother/find ways to identify mutts. I figure (in spite of the fact that it may have been posted elsewhere on this site since this thread) I should contribute (in the event that someone else stumbles across this) that we now know that citrinellum is a social benthic detritivore, while labiatus is a solitary crevice feeding active predator. In my "research" I have found that labiatus has a small upward fold/knob of tissue at the tip of the top lip (even in captive or immature specimens) that is completely absent in non crevice feeding amphilophus. This trait appears to carry down to mutts as well. I will continue my search for any other body proportions that can be used to diagnose the two species externally for the layman.
