|Scientific Name:||Oreochromis esculentus|
|Species Authority:||(Graham, 1928)|
|Red List Category & Criteria:||Critically Endangered A2bcde ver 3.1|
|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)|
This species has almost been eliminated from its previous range in lakes Victoria and Kyoga through predation, competitive exclusion and ecological displacement by introduced fishes (Twongo 1995, Nagayi Kalule 1999). The main population (in Lake Victoria) has declined by >80% over the past 20 years (FIRRI fishery records, Mugeriya, pers. comm.). The remaining population is limited to sub-populations in a few satellite lakes, which are themselves undergoing continued environmental degradation and heavy fishing pressure. This species is assessed as Critically Endangered.
|Range Description:||Present within the Lake Victoria drainage and Lake Kanyaboli. It has been introduced into several dams and waters, including the Pangani system (Lake Jipe). It is still present in some of the satellite lakes of Lakes Victoria and Kyoga. It is, however, virtually extinct from the main Lakes Victoria and Kyoga.|
Native:Kenya; Tanzania, United Republic of; Uganda
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and Ecology:||This species was originally (before competitive exclusion by the introduced species) confined to water less than 20 m deep and was most abundant in sheltered gulfs and bays where the bottom is composed of soft algaceous mud (Witte and de Winter 1995). It is a plankton feeder, using the mucus-trap mechanism combined with the combing action of the pharyngeal teeth. It is non selective all organisms of a size capable of being retained are passed into the stomach (Trewavas 1983). Breeding fish are found throughout the year and distinct spawning areas can be identified in the lake. Females brooding eggs often move off to the shelter of macrophyte beds or swampy areas. The young become independent at a length of about 15 mm when they are often found in channels in papyrus swamps (Trewavas 1983). Max Size: 248 mm SL (Trewavas 1983).|
|Major Threat(s):||Displacement by introduced fishes notably Nile perch and Nile tilapia. Heavy fishing pressure: over-fishing was reported by Horril (2000) as the cause for population decline, reduction in harvestable size and size at first maturity. Marked reduction of diatoms from the phytoplankton of Lakes Victoria and Kyoga at the expense of 'unpalatable' Cyanobacteria. Massive Typha species infestation of the spawning and nursery grounds. Increased siltation due to agricultural and cattle grazing practice in the area. Clearance of water-laden woodlands for agriculture (land encroachment), especially in the northwest, and for fuel wood. Pollution from domestic and agricultural effluents.|
|Conservation Actions:||No information available.|
Baillie, J. and Groombridge, B. 1996. 1996 IUCN Red List of Threatened Animals. International Union for Conservation of Nature, Gland, Switzerland.
Graham, M. 1929. The Victoria Nyanza and its fisheries. A report on the fishing surveys of Lake Victoria 1927–28. Crown Agents for the Colonies, London, United Kingdom.
Greenwood, P.H. 1966. The Fishes of Uganda. The Uganda Society, Kampala, Uganda.
Horril, C. 2000. Promotion of sustainable fisheries development at Nyumba ya Mungu Dam, Mwanga District. In: Unpublished consultancy report to Natual Resources Management and Buffer Zone Project.
IUCN. 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 04 May 2006.
Nagayi Kalule, J.F. 1999. Population Characteristics of Oreochromis esculentuin satellite lakes of the Victoria and Kyoga lakes basins. M. Sc. Thesis. Makerere University, Kampala, Uganda.
Nhwani, L.B. 1988. The trend of the fishery of Nyumba ya Mungu Dam. Tanzania Journal of Science 14: 77–104.
Trewavas, E. 1983. Tilapiine fishes of the genera Sarotherodon, Oreochromis and Danakilia. Cornell University Press, New York, United States.
Twongo, T. 1995. Impact of fish species introductions on the tilapias of Lakes Victoria and Kyoga. In: J. Pitcher & P.J.B. Hart (eds). The impact of species changes in African Lakes. Chapman and Hall, London, United Kingdom.
Welcomme, R.L. 1964. The habitat and habitat preferences of the young of the Lake Victoria Tilapia (Pisces: Cichlidae). Revue de Zoologie et de Botanique Africanes 70: 1–28
Witte, F. and de Winter, W. 1995. Appendix II. Biology of the major fish species of Lake Victoria. In: F. Witte & L.T. van Densen (eds). Fish Stocks and Fisheries of Lake Victoria. pp. 301–320. Samara Publishing Limited, Dyfed.
|Citation:||Twongo, T.K., Bayona, J.D.R. & Hanssens, M. 2006. Oreochromis esculentus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 17 April 2014.|
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