Because of the harsh aquatic environment, i.e. unpredictable erratic flows, droughts and episodic floods, the ORS (Orange River System) as a whole is relatively poor in indigenous freshwater fish species diversity. The fishes of the ORS have, over long periods of natural selection, adapted to a riverine environment and are mainly bottom feeders or predators. Because of these adaptations, they can benefit from the natural seasonal changes in environmental factors such as flow, temperature and turbidity. They generally spawn from the onset of spring through to autumn, when the river is in its annual high flow period, utilizing the flooded river banks and floodplains, conditions conducive to growth and survival of the young.
Presently, eight fish families are represented by 22 species in the ORS. Of these, three families, represented by five species are alien to Southern Africa, one species of an indigenous family is also alien and one species, indigenous to the subregion, of another family had been introduced to the ORS. The ORS thus only contains 15 indigenous freshwater fish species, representing five families – compare with KwaZulu-Natal’s ±85 species. Of the 15 indigenous fish species, six are endemic to the ORS with four of them Red Data listed. Of the remaining nine indigenous species, two are becoming threatened within the system, while the possibility exists that one could be an endemic subspecies. Freshwater fish species found between Augrabies Falls and the Orange River Mouth as below: