FISH POPULATIONS IN THE MIDDLE AND LOWER ORANGE RIVER, WITH SPECIAL REFERENCE TO THE EFFECTS OF STREAM REGULATION

SUMMARY

The results of two surveys, in March 1982 and September 1983, on the distribution and status of freshwater fish in the highly regulated section of the Orange River, from the P.K. Le Roux Dam wall to the mouth of the Orange River in the Republic of South Africa are presented. Collections are reported for the first time from the restricted diamondiferous areas in the extreme lower section of the Orange River. The known range of twelve freshwater fish species in the system has been extended as far down as 1,5 km from the mouth. Special attention is given to the Red Data Book species, Barbus hospes which occurs and breeds throughout the lower Orange River. It is suggested that stream regulation has probably been beneficial for this small, riverine Barbus species in contrast to B. paludinosus and B. trimaculatus which prefer quieter well vegetated habitats.

KEYWORDS:

• Stream regulation
• Orange River
• Barbus hospes
• Fish distribution
• Augrabies Falls
• Caridina nilotica