Oreochromis


Oreochromis is a large genus of oreochromine cichlids, 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. 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. 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.
Oreochromis are fairly robust fish, and medium–small to very large cichlids that can reach up to in total length depending on the exact species.
The earliest known member of this group is Oreochromis lorenzoi Carnevale, Sorbini & Landini, 2003 from the latest Miocene of Italy, suggesting that this genus naturally ranged as far north as southern Europe in prehistoric times.

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.
Oreochromis contains more than 30 species, and several undescribed forms exist. Judging from mtDNA sequence analysis, several clades seem to exist. Research is hampered because hybridization runs rampant in these fishes, which confounds mtDNA data, and the fast speed of evolution makes choice of appropriate nuclear DNA sequences difficult. 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 appear closer to Alcolapia than the remaining Oreochromis, and five other Oreochromis species appear to be as distant from the "core" Oreochromis as they are from Alcolapia. A potential solution is to merge Alcolapia into Oreochromis, as done by Catalog of Fishes.

Species

The 37 recognized species in this genus are:
  • Oreochromis alcalica
  • Oreochromis amphimelas
  • Oreochromis andersonii
  • Oreochromis angolensis
  • Oreochromis aureus
  • Oreochromis chungruruensis
  • Oreochromis esculentus
  • Oreochromis grahami
  • Oreochromis hunteri Günther, 1889
  • Oreochromis ismailiaensis Mekkawy, 1995
  • Oreochromis jipe
  • Oreochromis karomo
  • Oreochromis karongae
  • Oreochromis korogwe
  • Oreochromis latilabris
  • Oreochromis lepidurus
  • Oreochromis leucostictus
  • Oreochromis lidole
  • †Orechromis lorenzoi Carnevale, Sorbini & Landini, 2003
  • Oreochromis macrochir
  • Oreochromis malagarasi Trewavas, 1983
  • Oreochromis mortimeri
  • Oreochromis mossambicus
  • Oreochromis mweruensis Trewavas, 1983
  • Oreochromis ndalalani
  • Oreochromis niloticus
  • Oreochromis placidus
  • * Oreochromis placidus placidus
  • * Oreochromis placidus ruvumae
  • Oreochromis rukwaensis
  • Oreochromis saka
  • Oreochromis salinicola
  • Oreochromis schwebischi
  • Oreochromis shiranus Boulenger, 1897
  • * Oreochromis shiranus chilwae
  • * Oreochromis shiranus shiranus Boulenger, 1897
  • Oreochromis spilurus
  • * Oreochromis spilurus niger
  • * Oreochromis spilurus percivali
  • * Oreochromis spilurus spilurus
  • Oreochromis squamipinnis
  • Oreochromis tanganicae
  • Oreochromis upembae
  • Oreochromis urolepis
  • * Oreochromis urolepis hornorum
  • * Oreochromis urolepis urolepis
  • ''Oreochromis variabilis''