Summary
Young Tilapia on Lake Kariba show a marked preference for shallow water but this is complicated by fluctuating lake levels, the floating weed Salvinia auriculata and the Tigerfish Hydrocynus vittatus.
Tilapia nurseries found to date occur on shallow sloping shores predominently in the bush cleared areas and overlie Lower Karroo and Marly Sandstones. They are characterised by having a minimum of Salvinia coverage and a diversity of emergent and submerged aquatic plant growth arranged in fairly definate zones.
Rising lake levels provide the most favourable conditions for young Tilapia in the shallow, temporary nurseries. Receding water levels force the fish into Cerotophyllum and Potamogeton beds of the deeper water.
Tilapia do not leave cover until a length of between 17 cm and 19 cm is attained. Above this size they are considered reasonably safe from Hydrocynus. The impact on Tilapia of three nocturnal predators is considered insignificant at the present time.
Salvinia has the effect of causing lower oxygen tensions and retardation of essential submerged aquatic vegetation and is considered detrimental to the Tilapia fishery. Submerged aquatic plants are highly desirable to protect young Tilapia from predation during receding water levels.
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Donnelly, B.G. A preliminary survey of Tilapia nurseries on Lake Kariba during 1967/68. Hydrobiologia 34, 195–206 (1969). https://doi.org/10.1007/BF00141928
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DOI: https://doi.org/10.1007/BF00141928