Oreochromis is a large
genus of
oreochrominecichlids, fishes
endemic to
Africa and the
Middle East. A few species from this genus have been
introduced far outside their native range and are important in
aquaculture. Many others have very small ranges; some are seriously
threatened, and O. ismailiaensis and O. lidole possibly are
extinct.[1] Although Oreochromis primarily are freshwater fish of rivers, lakes and similar habitats, several species can also thrive in
brackish waters and some even survive in
hypersaline conditions with a salinity that far surpasses that of seawater.[1] In addition to overfishing and habitat loss, some of the more localized species are threatened by the introduction of other, more widespread Oreochromis species into their ranges. This is because they—in addition to competing for the local resources—often are able to
hybridize.[1]
Oreochromis are fairly robust fish, and medium–small to very large cichlids that can reach up to 9.4–61 cm (4–24 in) in total length depending on the exact species.[2]
Taxonomy
Species in this genus, as well as those in several other
oreochromine and
tilapiine genera, share the common name "
tilapia" and historically most were included in the genus Tilapia.[1]
Oreochromis contains more than 30
species, and several
undescribed forms exist. Judging from
mtDNAsequence analysis, several
clades seem to exist. Research is hampered because
hybridization runs rampant in these fishes, which confounds mtDNA data (
Wami tilapia is an example), and the fast speed of
evolution makes choice of appropriate
nuclear DNA sequences difficult.[3] A comprehensive
genetic study that included almost all the species, as well as the closely related Alcolapia, found that Oreochromis as currently defined is
paraphyletic. For example, two Oreochromis species (O. amphimelas and O. esculentus) appear closer to Alcolapia than the remaining Oreochromis, and five other Oreochromis species (O. angolensis, O. lepidurus, O. niloticus, O. schwebischi and O. upembae) appear to be as distant from the "core" Oreochromis as they are from Alcolapia.[1] A potential solution is to merge Alcolapia into Oreochromis,[1] as done by
Catalog of Fishes.[4]
Species
The 37 recognized species in this genus are:[2][5]
^Nagl, Sandra; Tichy, Herbert; Mayer, Werner E.; Samonte, Irene E.; McAndrew, Brendan J. & Klein, Jan (2001): Classification and Phylogenetic Relationships of African Tilapiine Fishes Inferred from Mitochondrial DNA Sequences. Molecular Phylogenetics and Evolution20(3): 361–374.
doi:
10.1006/mpev.2001.0979