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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.[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 compete for the resources—often are able to hybridize.[1]

Oreochromis
Oreochromis tanganicae (Günther).jpg
O. tanganicae
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cichliformes
Family: Cichlidae
Tribe: Oreochromini
Genus: Oreochromis
Günther, 1889
Type species
Oreochromis hunteri
Günther, 1889

Oreochromis are fairly robust fish, and medium–small to very large ciclids that can reach up to 9.4–61 cm (3.7–24.0 in) in total length depending on the exact species.[2]

TaxonomyEdit

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 mtDNA sequence 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]

SpeciesEdit

 
Oreochromis amphimelas of lakes, often saline, in north–central Tanzania
 
Oreochromis andersonii, a threatened species of south–central Africa
 
Oreochromis leucostictus of Albertine Rift Valley lakes and introduced elsewhere
 
Oreochromis lidole, a possibly extinct species of the Lake Malawi basin
 
Oreochromis macrochir, a threatened species of south–central Africa
 
Oreochromis mossambicus, a widespread species that also is introduced outside its native range
 
Oreochromis niloticus, a very widespread species that also is introduced outside its native range
 
Oreochromis squamipinnis, a threatened species of the Lake Malawi basin
 
Oreochromis variabilis, a threatened species of the Lake Victoria basin

The 33 recognized species in this genus are:[2]

ReferencesEdit

  1. ^ a b c d e Ford, A.G.P.; et al. (2019). "Molecular phylogeny of Oreochromis (Cichlidae: Oreochromini) reveals mito-nuclear discordance and multiple colonisation of adverse aquatic environments". Mol. Phylogenet. Evol. 136: 215–226. doi:10.1016/j.ympev.2019.04.008.
  2. ^ a b Froese, Rainer and Pauly, Daniel, eds. (2019). Species of Oreochromis in FishBase. September 2019 version.
  3. ^ 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 Evolution 20(3): 361–374. doi:10.1006/mpev.2001.0979