The karyotype of Oreochromis species is considered to be highly conserved,
with a diploid chromosome complement of 2n = 44. Here we show, by analysis of
mitotic and meiotic chromosomes, that the karyotype of O. karongae, one of
the Lake Malawi 'chambo' species, is 2n = 38. This difference in chromosome number
does not prevent the production of inter-specific hybrids between O. niloticus
(2n = 44) and O. karongae (2n = 38). Analysis of the meiotic chromosomes of
the O. niloticus x O. karongae hybrids indicates that three separate
chromosome fusion events have occurred in O. karongae. Comparison of the
O. karongae and O. niloticus karyotypes suggests that these consist
of one Robertsonian fusion and two fusions of a more complex nature.