M.Sc. / The tigerfish, Hydrocynus vittatus, is one of the most sought-after game fish in Southern Africa, and a vital source of protein and income in contiguous communities. Unfortunately, this species has been placed on the protected species list, alongside the infamous great white shark (Carcharodon carcharias). The loss of this species will not only be disadvantageous to local communities, but will also have a damaging impact on the Southern African tourism industry. After reviewing all available literature on tigerfish, it was noted that studies on the genetics, morphology, distribution, age, growth and maturity were severely lacking. Research on the Pongolapoort Dam and Phongolo River tigerfish was also practically nonexistent. The aims of this study were therefore to: (1) analyse the genetic variation and diversity of five Southern African tigerfish populations and comment on the use of the various populations as possible candidates for restocking; (2) assess whether the genetic composition and caudal colour can be linked to the biogeography of the species; (3) determine the growth patterns of tigerfish otoliths and establish the best ageing technique for this species; and (4) determine the age structure of tigerfish from the Pongolapoort Dam in KwaZulu-Natal, South Africa. Before analysing the genetic composition of various tigerfish populations, it was hypothesised that individuals from the Okavango and Phongolo systems would possess the highest and lowest heterozygosity, respectively. Tigerfish from the Olifants River would be the best choice of brood stock, should population restocking become necessary. The muscle and liver tissues of 117 tigerfish from the Upper Zambezi, Okavango Delta, Olifants and Phongolo Rivers and Pongolapoort Dam, were assessed by starch gel electrophoresis.

Ph.D. / Since the systematics in the family Characidae from southern Africa were only reliant on some morphological traits, the determination of the genetic variation, genetic distances and phylogenetic relationships using different molecular techniques led to the formulation of this study. The first aim of the study was to describe the amount and pattern of genetic variation withi~ and between populations. The analysis of the isozymes provided the first account of the amount. pattern and distribution of genetic variation within this family. A general introduction on the history, distribution, descriptions, taxonomy and some ecological notes from the literature on southern African Characidae species is included in Chapter l. The second chapter dealt with the Hydrocynus genus that represents, morphologically, the largest member of this family. Other members of the Characidae family are relatively small species that do not exceed 300g. Twenty-five enzyme coding loci in two populations of H. vittatus, from Namibia and South Africa, were analyzed by horizontal starch gelelectrophoresis. Electrophoretic analysis of liver. white muscle, heart and testis samples revealed genetic variation at 20% (Upper Zambezi River. Namibia) and 36% (Oiifants River. South Africa) of the protein coding loci studied. Average heterozygosity values ranged from l .9% (Upper Zambezi River) to 4.6% (Oiifants River), with a genetic distance value of 0.005 between these populations. The low amount of genetic variability in the former population compared to that of other fish species from the same geographical area, and to that of H. vittatus from the Olifants River. can be attributed to restricted gene flow due to isolation. Although morphological differences exist between the two populations. the extent thereof is not sufficient to regard them as subspecies.