Ph.D (Zoology) / The Characiformes, which are widespread in Africa and the Neotropical Region, comprise a broad series of species with strong oral teeth, of which numerous are top predators in their respective areas of distribution. This is the case with the six Hydrocynus species (Alestidae), which are endemic to African fresh waters (Skelton, 2001) and better known as tigerfish, owing to their striped colour pattern and prominent oral teeth (Jubb, 1967). As top predators they play a significant role in the functioning of riverine eco-systems, in particular as regards the transfer of energy from the floodplains to the main rivers (Winemiller & Kelso-Winemiller, 1994). Also as top predators they contribute to the maintenance of diversity in these eco-systems and to stabilize the energy acquired by their prey during their growth in the eutrophic floodplain. They also contribute substantially to inland fisheries, notably to the recreational side, since they are deservedly ranked among the most spectacular freshwater game species. Despite their ecological importance there is a dearth of knowledge on their ecology and behaviour, accept for a few dedicated studies (Baras et al., 2002). Tigerfish have a tropical distribution, but some species, such as Hydrocynus vittatus ranges to the southern limit of the inter-tropical region and is found in South African waters. In South Africa, H. vittatus occurs in the lowveld reaches of coastal systems north of the Phongolo River (Skelton, 2001). The species was formerly reported at altitudes greater than 300 m above sea level in Mpumalanga, Swaziland and Kwazulu Natal (Gaigher, 1969). Nowadays its distribution is restricted to the lower reaches of these rivers. In the Incomati River system, most historical records suggest that H. vittatus occurred up to the confluence of the Komati and Mlumati rivers, a distance of 50 km upstream from Komatipoort...