the fish here in question is positively some type of Thorichthys (firemouth cousin). the trick is narrowing down which one because several of them look alike as juveniles. I'd be willing to bet it's one of the Mixtecos and my money is on Thorichthys sp. 'mixteco gold' because at one time or another I've kept all 3 mixtecos. The mixteco blue and mixteco green look similar as juveniles, but I noticed when keeping them that the mixteco gold looked a little different. the black mid-lateral line was rarely present and neither was the black spot on the back half of the fish's side. the mixteco golds (as juveniles) have a pinkish background with yellow near and definitely behind the gill plates with a turqoise spangling all over. they also have a red-tipped dorsal fin. females will have a black blotch in the dorsal and this is true of all three mixtecos. the pic in the profile I linked to is of a 4" male which simply looks like a larger version of the mystery fish here in question.