Overview

Comprehensive Description

Biology

Occurs at temperatures ranging from 23.0-28.0 °C (Ref. 3). Occasionally forms schools. Is mainly diurnal. Adults feed predominantly on bottom algae, some of the planktonic organisms that are found in their stomachs are probably those which have settled on the bottom or were washed shorewards from open waters but they do feed directly on plankton (Ref. 2).
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Distribution

Range Description

Lake Victoria drainage (endemic). It has not been recorded in the Tanzanian part of the Lake since the 1990s (Seehausen and Bouton 1997, Mkumbo 1999). The species is, however, still found in some localized portions of the lake and in satellite lakes, mainly Burigi, Katwe, and Kirumi pool (Katunzi and Kishe 2002). It is also found in Nyumba ya Mungu Dam and several inland ponds following probable introductions.
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Eastern Africa: Lake Victoria and associated rivers.
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Africa: Lake Victoria and its affluent rivers; the Victoria Nile above the Murchison Falls; Lakes Kyoga, Kwania and Salisbury (Ref. 5166). It is strongly declining or has disappeared in many areas of the Lake Victoria drainage (Ref. 52331).
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Physical Description

Morphology

Dorsal spines (total): 16 - 18; Dorsal soft rays (total): 10 - 12; Analspines: 3; Analsoft rays: 9 - 11; Vertebrae: 29 - 31
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Size

Maximum size: 267 mm SL
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Max. size

30.0 cm SL (male/unsexed; (Ref. 34290))
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Diagnostic Description

Margin of the dorsal fin orange in females and non-breeding males; intense orange to scarlet in breeding males. Profile convex immediately before the eye. Usually 2 rows of scales on cheek. Caudal not heavily scaled. Preserved specimens often show 2-3 vague dark mid-lateral blotches and one on top of the peduncle. Body color grey-green (Ref.4967).
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Type Information

Cotype for Tilapia variabilis
Catalog Number: USNM 86646
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Locality: Entebbe, L. Victoria, Uganda, Africa
  • Cotype:
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Most abundant on exposed and sandy shores where there is considerable water movement. It also occurs in the calm waters of water lily swamps (Lowe McConnell 1956). Found at a depth range of 0–40 m but most commonly in water less than 10 m deep (Witte and de Winter, 1995). The young fish feed on planktonic algae and may ingest small copepods. The adults feed predominantly on bottom algae but they also feed directly on plankton (Trewavas, 1983) and may graze algae from rocks and aquatic plants (Witte and de Winter 1995). It spawns on firm or sand habitats and breeding males may occasionally be seen guarding their circular nests in water a few feet deep at the edge of the lake. Young are brooded until about 15 mm long. Brooding females have been caught in the rushes and among vegetation near the edges of the lake (Lowe McConnell 1956). Max Size: 246 mm SL (Trewavas 1983).

Systems
  • Freshwater
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Depth: 4 - 49m.
From 4 to 49 meters.

Habitat: demersal.
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Environment

benthopelagic; freshwater; depth range 4 - 49 m
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Trophic Strategy

Present to 13 meters in Lake Victoria. The species is also noted for entering rivers from the lakes. Between 8 and 17 cm they move about in schools; schooling is less marked after reaching 17 cm. (See also Ref. 3736)
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Diseases and Parasites

Trypanosoma Infestation 2. Parasitic infestations (protozoa, worms, etc.)
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Trypanosoma Infection. Parasitic infestations (protozoa, worms, etc.)
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Sporozoa-infection (Myxobolus sp.). Parasitic infestations (protozoa, worms, etc.)
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Lymphocystis Disease. Viral diseases
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Dactylosoma Infection 1. Parasitic infestations (protozoa, worms, etc.)
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Cichlidogyrus Infestation 2. Parasitic infestations (protozoa, worms, etc.)
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Cichlidogyrus Infestation 10. Parasitic infestations (protozoa, worms, etc.)
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Cichlidogyrus Disease. Parasitic infestations (protozoa, worms, etc.)
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Life History and Behavior

Life Cycle

Nests are built on sandy bottoms in shallow waters. Each nest consists of a central shallow saucer 13-15 cm in diameter, around which is a circle of small pits. This structure is the center of a larger pit, 30-39 cm in diameter. Breeding pair makes the T-stand. Female lays batches of eggs; picks them up and sucks at the male's genital tassel.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
CR
Critically Endangered

Red List Criteria
B1ab(i,ii,iii,iv,v)

Version
3.1

Year Assessed
2006

Assessor/s
Twongo, T.K., Bayona, J.D.R. & Hanssens, M.

Reviewer/s
Snoeks, J. (Freshwater Fish Red List Authority) & Darwall, W. (Freshwater Biodiversity Assessment Programme)

Contributor/s

Justification
This species has suffered a large reduction in extent of occurrence and is now restricted to a few small satellite lakes (estimated extent of occurrence <100 km²) having been virtually eliminated from its original range in Lakes Victoria and Kyoga through predation, competitive aggression and ecological displacement by introduced fish species. Its current distribution is highly fragmented and its remaining habitat continues to be degraded and it is subject to heavy fishing pressure.

History
  • 1996
    Vulnerable
    (Baillie and Groombridge 1996)
  • 1996
    Vulnerable
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Population

Population
The population has declined. It supported a commercial fishery in Lake Victoria prior to the nineteen fifties but later declined to low levels prompting restocking (Oguto Ohwayo 1990). Trawl surveys during 1969/70 established catch rates of 1.5 kg/hr (Mkumbo 1999) but these rates have not been possible since that time as it has been virtually eliminated from main Lake Victoria and Lake Kyoga due to predation by the introduced Nile perch (Ogutho-Ohwayo 1990), and through ecological displacement by introduced Nile tilapia and Tilapia zilii (Twongo 1995). Present-day sub-populations are highly fragmented within the satellite lakes, where they are free from predation by the Nile perch.

Population Trend
Decreasing
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Threats

Major Threats
Over-fishing, particularly using illegal methods and gear. Competition for habitats and food with exotic species (introduced Nile tilapia), and predation by the introduced Nile perch.
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Critically Endangered (CR) (B1ab(i,ii,iii,iv,v))
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Management

Conservation Actions

Conservation Actions
No information available.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial; aquaculture: experimental; aquarium: commercial
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Wikipedia

Oreochromis variabilis

Oreochromis variabilis, the Victoria tilapia, is a species of cichlid native to Lake Victoria and its tributaries, Lake Kyoga, Lake Kwania and Lake Salisbury as well as being found in the Victorian reach of the Nile above Murchison Falls. This species can reach a length of 30 centimetres (12 in) SL. This species is important to local commercial fisheries as well as being potentially important in aquaculture. It is also found in the aquarium trade.[2]

References [edit]

  1. ^ Twongo, T.K., Bayona, J.D.R. & Hanssens, M. 2006. Oreochromis variabilis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 10 May 2013.
  2. ^ Froese, Rainer and Pauly, Daniel, eds. (2013). "Oreochromis variabilis" in FishBase. April 2013 version.
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