I am sure this is one of the Malawi mbuna , but there are a great many species with males with this BB colour pattern, and most of them have local variants which are very hard to tell apart. My semi-educated guess, based largely on body shape, is that this might be one of the Cynotilapia or Labidochromis species, but I could be wrong and I don't think I can speculate more. See Cynotilapia and the other pages on that site if you dare to go further.
