Oreochromis urolepis hornorum
Encyclopedia
The Wami tilapia is a tilapiine cichlid
that grows to over 20 cm in length and is considered a useful food fish
in Tanzania
and the island of Zanzibar
, where it may have been introduced by man. It is tolerant of brackish water and grows well in saline pools, making it particularly suitable for aquaculture by communities living close to the sea. Like other tilapia
it is an omnivore
and will feed on algae, plants, small invertebrates, and detritus. The common name refers to the Wami River
.
Formerly considered a separate species
, it is at present merged with the Rufigi tilapia and thus the scientific name is Oreochromis urolepis hornorum. The obsolete scientific name Tilapia hornorum is also still seen not infrequently. However, mtDNA sequence
analysis has found that the mitochondrial genome is possibly very similar to that of Sarotherodon galilaeus (Nagl et al. 2001); it might be moved to Sarotherodon based on these results. On the other hand, hybridization is quite common in tilapiines and hybrids even between not too closely related species may be fertile.
In captivity, Wami tilapia have been hybridised with the Mozambique tilapia (Oreochromis mossambicus). The resulting fish produce broods almost entirely consisting of males. Male tilapia grow faster and to a more uniform size than females, making them particularly useful for aquaculture
http://edis.ifas.ufl.edu/FA012. Note that based on the mtDNA study by Nagl et al. (2001), the Mozambique and Wami tilapias do not appear to be closely related.
3 possibilities may explain this discrepancy: Either, the Wami tilapia and its closest relatives (such as the Rufigi and Blue Tilapias) belong into Sarotherodon. Alternatively, they are correctly placed in Oreochromis but their ancestors hybridized with some ancestral Sarotherodon. Given that only a single specimen was analyzed, it is theoretically also possible that the Wami tilapia is a cryptic species complex
. This is less likely because cryptic speciation requires barriers to gene flow
which in the tilapiines are not well-developed.
The mtDNA data of Klett & Meyer (2002) places the Rufigi tilapia into Oreochromis (though not close to the Mozambique Tilapia, but rather to Oreochromis amphimelas
). This would seem to support the second hypothesis - maternal gene flow from Sarotherodon to Oreochromis; whether this is correct or not, it amply illustrates that mtDNA sequences are not a reliable indicator of phylogenetic relationships in these fish.
Cichlid
Cichlids are fishes from the family Cichlidae in the order Perciformes. Cichlids are members of a group known as the Labroidei along with the wrasses , damselfish , and surfperches . This family is both large and diverse. At least 1,300 species have been scientifically described, making it one of...
that grows to over 20 cm in length and is considered a useful food fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
in Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
and the island of Zanzibar
Zanzibar
Zanzibar ,Persian: زنگبار, from suffix bār: "coast" and Zangi: "bruin" ; is a semi-autonomous part of Tanzania, in East Africa. It comprises the Zanzibar Archipelago in the Indian Ocean, off the coast of the mainland, and consists of numerous small islands and two large ones: Unguja , and Pemba...
, where it may have been introduced by man. It is tolerant of brackish water and grows well in saline pools, making it particularly suitable for aquaculture by communities living close to the sea. Like other tilapia
Tilapia
Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...
it is an omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
and will feed on algae, plants, small invertebrates, and detritus. The common name refers to the Wami River
Wami River
The Wami River lies entirely within the African nation of Tanzania in the Pwani Region and Morogoro Region in eastern Tanzania. Its source is specified in the Kaguru Mountains and it flows East entering the Indian Ocean west of Zanzibar. But its catchment area extends from the Kinyasangwe River to...
.
Formerly considered a separate species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, it is at present merged with the Rufigi tilapia and thus the scientific name is Oreochromis urolepis hornorum. The obsolete scientific name Tilapia hornorum is also still seen not infrequently. However, mtDNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
analysis has found that the mitochondrial genome is possibly very similar to that of Sarotherodon galilaeus (Nagl et al. 2001); it might be moved to Sarotherodon based on these results. On the other hand, hybridization is quite common in tilapiines and hybrids even between not too closely related species may be fertile.
In captivity, Wami tilapia have been hybridised with the Mozambique tilapia (Oreochromis mossambicus). The resulting fish produce broods almost entirely consisting of males. Male tilapia grow faster and to a more uniform size than females, making them particularly useful for aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
http://edis.ifas.ufl.edu/FA012. Note that based on the mtDNA study by Nagl et al. (2001), the Mozambique and Wami tilapias do not appear to be closely related.
3 possibilities may explain this discrepancy: Either, the Wami tilapia and its closest relatives (such as the Rufigi and Blue Tilapias) belong into Sarotherodon. Alternatively, they are correctly placed in Oreochromis but their ancestors hybridized with some ancestral Sarotherodon. Given that only a single specimen was analyzed, it is theoretically also possible that the Wami tilapia is a cryptic species complex
Cryptic species complex
In biology, a cryptic species complex is a group of species which satisfy the biological definition of species—that is, they are reproductively isolated from each other—but whose morphology is very similar ....
. This is less likely because cryptic speciation requires barriers to gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
which in the tilapiines are not well-developed.
The mtDNA data of Klett & Meyer (2002) places the Rufigi tilapia into Oreochromis (though not close to the Mozambique Tilapia, but rather to Oreochromis amphimelas
Oreochromis amphimelas
Oreochromis amphimelas is a species of fish in the Cichlidae family. It is endemic to Tanzania. Its natural habitats are intermittent freshwater lakes and saline lakes.-Source:* Bayona, J.D.R. 2005. . Downloaded on 4 August 2007....
). This would seem to support the second hypothesis - maternal gene flow from Sarotherodon to Oreochromis; whether this is correct or not, it amply illustrates that mtDNA sequences are not a reliable indicator of phylogenetic relationships in these fish.