Abstract
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.