|Scientific Name:||Oreochromis andersonii (Castelnau, 1861)|
Tilapia kafuensis Boulenger, 1912
|Red List Category & Criteria:||Vulnerable A3e ver 3.1|
|Assessor(s):||D. Tweddle & Marshall, B.E.|
|Reviewer(s):||Snoeks, J. (Freshwater Fish Red List Authority) & Darwall, W. (Freshwater Biodiversity Assessment Programme)|
Insufficient data are available on the apparent declines in abundance, but anecdotal evidence suggests a major decline in stocks on the Barotse floodplain since the 1960s as a result of heavy fishing pressure. The rapid spread of alien O. niloticus through the Kafue system will have had a major impact though data are lacking, and the species is now being promoted for aquaculture in the Upper Zambezi catchment. Under criterion A3e, a population reduction of up to 100% is projected in areas where O. niloticus invades. In these area (i.e., in Zambia as a whole), the species should be classed as CR A3(e). It seems inevitable that the O. niloticus will continue to spread throughout the range of O. andersonii unless drastic steps are taken immediately.
At present, the Okavango population is not immediately threatened, but this system is intermittently linked to the Zambezi and thus it is inevitable that O. niloticus will invade the system unless a barrier is constructed across the Selinda Spillway to prevent migration.
O. andersonii is also recorded from the Cunene River, where O. niloticus does not yet occur. The alien species Oreochromis mossambicus (Peters, 1852) is, however, being extensively cultivated in Namibia and may hybridise with O. andersonii if it escapes in to the Cunene.
Establishing refuges in lakes that are not directly connected to the main rivers or to aquaculture establishments may allow small populations to survive. For this reason, and the possibility that the Cunene population may be secure at present, the species is assessed as Vulnerable globally.
|Range Description:||This species occurs in the upper Zambezi, as well as the Kafue, Okavango and Cunene Rivers. Occasionally also recorded from the Middle Zambezi (Skelton 2001).
In East Africa, the species was introduced in Kenya in 1980 from Botswana (Motiti Pan, Okavango drainage) by I. Parker for aquaculture purposes. It was introduced to a dam near Nairobi and it is possible that some specimens found their way into the Nairobi River system.
Native:Angola; Botswana; Namibia; Zambia; Zimbabwe
Introduced:Congo, The Democratic Republic of the; Kenya; South Africa; Tanzania, United Republic of
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Fairly common and widespread in the Okavango and Upper Zambezi Rivers, although depleted by fishing in some areas such as the Barotse floodplain.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Adults are found mainly in deeper pools and main river channels. Juveniles and sub-adults are found in a variety of habitats in rivers and floodplain lagoons, large open swamps, and, more rarely small tributaries of the rivers. Feeds on detritus, diatoms and zooplankton. Males excavate large, saucer-shaped nests, females mouthbrood the eggs and fry. Multiple broods are raised during the warmer months. Lives for up to 11 years.|
The spread of alien Oreochromis niloticus (L.) as a result of aquaculture introductions in the Kafue and Upper Zambezi catchments is a major threat to the survival of O. andersonii throughout its range (Tweddle et al. 2004). Oreochromis niloticus has caused the extinction of O. esculentus (Graham) and O. variabilis (Boulenger) in Lake Victoria. It has also replaced O. mortimeri (Trewavas) in Lake Kariba, has spread throughout the Kafue Flats in Zambia and is rapidly replacing O. mossambicus (Peters) in the Limpopo system in southern Africa.
Increasing fishing effort and increasingly widespread use of small-meshed fishing nets has depleted stocks in many areas, such as the heavily-populated areas of the Barotse Floodplain on the Upper Zambezi River in Zambia. Floodplain lagoons no longer provide refugia as they are all intensively seine netted.
A commercial gillnet fishery in the Panhandle area of the Okavango Delta also targets this species.
|Conservation Actions:||Nile tilapia should be urgently removed from ponds in the Upper Zambezi system in northern Zambia and replaced by O. andersonii. Attempts should be made to prevent the spread of O. niloticus and establish refuges for O. andersonii and other species.|
|Citation:||D. Tweddle & Marshall, B.E. 2007. Oreochromis andersonii. The IUCN Red List of Threatened Species 2007: e.T60623A12385801.Downloaded on 23 October 2017.|
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