Tweddle, D. (Freshwater Fish Red List Authority) & Darwall, W. (Freshwater Biodiversity Assessment Unit)
Threatened by hybridization with the rapidly spreading Oreochromis niloticus. Oreochromis niloticus is being spread by anglers and for aquaculture. Hybridization is already occurring throughout the northern part of the species' range, with most of the evidence coming from the Limpopo River system. In terms of locations the threat of Oreochromis niloticus is widespread, but probably more than 50% of the locations are not yet affected. Given the rapid spread of O. niloticus it is anticipated that this species will qualify as threatened under Criterion A due to rapid population decline through hybridization. The species is therefore assessed as Near Threatened.
Lower Zambezi, Lower Shire and coastal plains from Zambezi delta to Algoa Bay. Occurs southwards to the Bushmans River in the eastern Cape and in the Transvaal in the Limpopo system (Skelton 2001). Widely dispersed beyond this range to inland regions and to the south west and west coastal rivers including the lower Orange and rivers of Namibia. Introduced to tropical and warm temperate localities throughout the world.
Malawi; Mozambique; South Africa (Eastern Cape Province, KwaZulu-Natal); Swaziland; Zambia; Zimbabwe
Occurs in all but fast-flowing waters; thrives in standing waters. Further south in its range it is most common in blind estuaries and coastal lakes where it tolerates brackish and marine environments. Feeds on algae, especially diatoms, and detritus, large individuals also take insects and other invertebrates. Breeds in summer, females raising multiple broods every 3 to 4 weeks during a season. Males construct a saucer-shaped nest on sandy bottoms: the female mouthbroods the eggs, larvae and small fry. Juveniles shoal in shallow water. Prone to stunting under adverse or crowded conditions (Skelton 2001).
The Nile tilapia, Oreochromis niloticus, is invading its natural range in the Zambezi and Limpopo systems. Hybridisation is occurring in the Limpopo system and pure O. mossambicus are likely to become extirpated in those systems through competition and hybridisation.