Allozyme variation in two populations of Hydrocynus vittatus (Pisces, Characidae)

The isozymes described in this study provide the first account of the amoun t, pattern and distribution of genetic variation within this genus. Twenty- five enzyme coding loci in two populations of H. vittatus, from Namibia aci d South Africa, were analysed by horizontal starch gel-electrophoresis. Ele ctrophoretic analysis of liver, white muscle, heart and testis samples reve aled genetic variation at 20% (Upper Zambezi River, Namibia) and 36% (Olifa nts River, South Africa) of the protein coding loci studied. Average hetero zygosity values ranged from 1.9% (Upper Zambezi River) to 4.6% (Olifants Ri ver), with a genetic distance value of 0.005 between these populations. The low amount of genetic variability in the former population compared to tha t 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 owing to isolation. Although morphological differences exist between the t wo populations, the extent thereof is not sufficient to regard them as subs pecies.