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Oreochromis variabilis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA ACTINOPTERYGII PERCIFORMES CICHLIDAE

Scientific Name: Oreochromis variabilis
Species Authority: (Boulenger, 1906)

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(i,ii,iii,iv,v) ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
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)
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

Geographic Range [top]

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.
Countries:
Native:
Kenya; Tanzania, United Republic of; Uganda
Range Map: Click here to open the map viewer and explore range.

Population [top]

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

Habitat and Ecology [top]

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

Threats [top]

Major Threat(s): 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.

Conservation Actions [top]

Conservation Actions: No information available.

Citation: Twongo, T.K., Bayona, J.D.R. & Hanssens, M. 2006. Oreochromis variabilis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 22 December 2014.
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