''Oreochromis variabilis'', the Victoria tilapia, is a species of African

cichlid Cichlids () are a large, diverse, and widespread family of percomorph fish in the family Cichlidae, order Cichliformes. At least 1,760 species have been scientifically described, making it one of the largest vertebrate families, with on ...

native to

Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropics, tropical lake, and the world's second-largest fresh water lake by surface are ...

and its

tributaries A tributary, or an ''affluent'', is a stream or river that flows into a larger stream ('' main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which the ...

Lake Kyoga Lake Kyoga or Lake Kioga (literally 'the place of bathing' in Runyoro language) is a large shallow lake in Uganda, about in area and at an elevation of 1,033 metres. The Victoria Nile flows through the lake on its way from Lake Victoria to Lake ...

Lake Kwania Lake Kwania is in the districts of Lira, Apac and Amolatar in the Northern Region of Uganda. It is part of a large wetland along the White Nile (Victoria Nile) between Lake Victoria and Lake Albert. The wetland, which includes Lake Kwania, the ...

, and Lake Bisina (Salisbury), as well as being found in the

Victoria Nile The White Nile ( ') is a river in Africa, the minor of the two main tributary, tributaries of the Nile, the larger being the Blue Nile. The name "White" comes from the clay sediment carried in the water that changes the water to a pale color. ...

above

Murchison Falls Murchison Falls, also known as Kabalega Falls, is a waterfall in Uganda, located at the apex of Lake Albert on the White Nile. At the top of Murchison Falls, the Nile forces its way through a gap in the rocks, only wide, and tumbles , before fl ...

. This species can reach a

standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

of . This species is important to local

commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...

and is potentially important in

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

. It is also found in the

aquarium An aquarium (: aquariums or aquaria) is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. fishkeeping, Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquati ...

trade. Despite its common name, it is not the only tilapia native to Lake Victoria. The equally threatened '' O. esculentus'' has a similar distribution.

Description

''Oreochromis variabilis'' has typical characteristics of a cichlid fish: long

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

with both spiny and soft rays, a broken lateral line, a single pair of nostrils and a single lower pharyngeal bone. Like other typical 'tilapias', it has relatively small closely packed teeth, numerous

gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of th ...

s and juveniles have a dark 'tilapia spot' at the base of the soft-rayed part of the dorsal fin. Like other members of the subgenus ''Nyasalapia'', the mature males develop a long, branched genital tassel and construct complex display structures or bowers on the bottom mud, characterised by a raised central platform, in contrast to the simple saucer-shaped pits excavated by other ''Oreochromis''. They also lack the enlarged jaws seen in mature males of the '' Oreochromis mossambicus'' group. Courting males are typically black (sometimes with a blue-green sheen), with bright red margins to the dorsal and tailfins. These characteristics are shared with the allopatric species ''O. malagarasi'' (

Lake Tanganyika Lake Tanganyika ( ; ) is an African Great Lakes, African Great Lake. It is the world's List of lakes by volume, second-largest freshwater lake by volume and the List of lakes by depth, second deepest, in both cases after Lake Baikal in Siberia. ...

catchment) and '' O. rukwaensis'' (

Lake Rukwa Lake Rukwa is an endorheic lake located in the Rukwa Valley of Rukwa Region, Songwe Region and Katavi Region in southwestern Tanzania. The lake is the third largest inland body of water in the country. Geography The alkaline Lake Rukwa lies ...

, and recently reported also from the upper part of the Great Ruaha catchment). An apparently unique feature of ''O. variabilis'', and the source of its name, is its colour polymorphism. A small proportion of individuals of both sexes, although mainly females, show a disrupted

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

distribution, resulting in a pale orange or whitish fish with irregular dark blotches on the fins and body. This kind of pattern is known in

haplochromine __NOTOC__ The haplochromine cichlids are a tribe of cichlids in subfamily Pseudocrenilabrinae called Haplochromini. This group includes the type genus ''Haplochromis'' plus a number of closely related genera such as '' Aulonocara'', '' Astatotila ...

cichlid fishes from African great lakes (notably the Lake Malawi '

mbuna Mbuna (pronounced Mmm-boo-nah ) is the common name for a large group of African cichlids from Lake Malawi, and are members of the haplochromine tribe within the family Cichlidae. The name ''mbuna'' means "rockfish" in the language of the Tonga pe ...

' cichlids), where it is again mainly expressed in females. It bears some resemblance to the 'red tilapia' artificially selected in the

industry. These were known as 'Maradadi' among at least some of the fisherfolk on Lake Victoria, when this species was still an important food fish on the lake. ''Oreochromis variabilis'' also has a rather distinctive head profile, with a 'bump' just above the eyes, rather like the

Lake Malawi Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, () is an African Great Lakes, African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. It is ...

'chambo' species (males of which lack red fin margins), but less strongly expressed in ''O. rukwaensis'' and ''O. malagarasi''.

Reproductive biology

Like all other known ''Oreochromis'', ''O. variabilis'' is a maternal

mouthbrooder Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a va ...

. Males are conspicuously coloured and aggregate in shallow waters, where they aggressively defend territories centred around their courtship bower. Females visit a number of males, laying batches of eggs with several, but rejecting many others. Females quickly pick up the eggs in their mouths and carry them for several weeks before releasing them to feed. Young are guarded in shallow weedy or rocky areas and may be re-admitted to their mother's mouth until they reach a length of about 15mm. In Lake Victoria, fishes were recorded as maturing at around 20 cm TL (total length), but in smaller water bodies, they might breed at about 16 cm TL. Females produce around 320–550 eggs, averaging around 2.5–4.5 cm in diameter. The bowers built by males are complex structures, with a raised central shallow saucer about 13–25 cm in diameter with a rim around 2 cm high, surrounded by 6–12 small pits, all contained within a larger pit, 30–90 cm in diameter, with a raised perimeter wall. Victoria_tilapia_2

Ecology

In its natural habitat, ''O. variabilis'' frequents shallow areas, both rocky and weedy, while the congeneric ''O. esculentus'' dominated the offshore habitats. Juveniles have been reported to feed on

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

, while adults mainly feed on bottom sediments or biofilms on rocks and other hard surfaces.

Current status of populations

The species is listed as near threatened by IUCN, with population declines attributed to the introduction of predatory

Nile perch The Nile perch (''Lates niloticus''), also known as the African snook, Goliath perch, African barramundi, Goliath barramundi, Giant lates or the Victoria perch, is a species of freshwater fish in family Latidae of order Perciformes. It is wides ...

and competing non-native tilapias. However, populations continued to be reported from satellite lakes in the catchment which had remained unstocked with these exotics. More recently, in 2016, individuals were recorded on the rocky offshore island of Makobe in the Tanzanian part of the lake.

References

{{Taxonbar, from=Q2258902 variabilis Fish of Lake Victoria Freshwater fish of Tanzania Taxonomy articles created by Polbot Fish described in 1906