These are mature adults on the source images, not juveniles. Also look at maculated D and A fins. The dealer speaks about Mtoto's polymorphism and two colour variations one of which keeps brightly yellow coloration at adult age. 3-4 cm juveniles are yellow.
Last edited by Grange on Mon Oct 12, 2009 4:08 pm, edited 1 time in total.
It's the "Moshi Yellow" from the Mahale area in Tanzania, see the eggspots in both dorsal and anal fin. Besides a nice O. nasuta is seen in the foreground in the second photo, with coloration very typically of the the Mahale area.