Abstract
M.Sc.
The Vaal Dam subcatchment is located in the upper reaches of the Vaal River. As a result
the water quality is reasonably good. In contrast the Vaal River Barrage catchment
includes the PWV area, resulting in poorer water quality. During this study, a fish Health
Assessment Index (HAI) successfully tested in previous studies on the Olifants River
System was applied to the Vaal River System. The aim was to determine if the HAI could
distinguish between the Vaal Dam and Vaal River Barrage with regards to water quality. Surveys were conducted bimonthly from November 1998 to February 2000.
Physical water quality variables were measured. Water and sediment samples were also
collected and analyzed (Institute for Water Quality Studies, Department of Water Affairs
and Forestry) to verify the HAI results. Rand Water Board and the Department of Water
Affairs and Forestry also made water quality data available. Twenty sharptooth catfish,
Clarias gariepinus, were collected from both localities with the aid of gill nets. Fish were
checked for external parasites on the boat. On land fish were weighed and measured, after
which blood was drawn and slime smears made. Blood and slime smears were examined
under a light microscope for parasites. The HAI examination was performed after
severing the spinal cord. Internal parasite numbers were recorded. From the parasite data
collected infestation statistics were calculated. Four variations of the Parasite Index (PI)
were incorporated in the HAI and results compared. During each survey gill arch, gill
filament, muscle, skin and liver tissues were collected from each fish. These were
analyzed for strontium, aluminium, chromium, manganese, iron, lead, copper, zinc and
nickel concentrations using atomic absorption spectrophotometry. Differences in water and sediment trace metal concentrations between localities
were small. Metal concentrations in fish tissues recorded from both localities were also
almost identical. Possible explanations for this trend were discussed in the relevant
section. Highest metal concentrations were generally recorded in gill tissue followed by
liver, skin and muscle. Physical water quality variables (salinity and conductivity), and
macro water analysis (e.g. phosphate and nitrate) indicated that water quality at the Vaal
River Barrage was poorer. The HAI confirmed this. Higher index values were recorded from the Vaal River
Barrage, with the converse being true for the Vaal Dam. Regression analysis indicated that plasma protein, haematocrit and the index value obtained using the Inverted Parasite
Index, most successfully predicted (70 %) from where a randomly chosen fish were
collected. When viewing index values obtained using the four versions of the PI, all four
distinguished between localities. The discriminatory ability of the Inverted PI was
slightly higher than that of the other PI's.
It is concluded that the HAI distinguished successfully between the Vaal Dam and
Vaal River Barrage on the grounds of water quality. Poor fish health correlated with
decreasing water quality (salinity and eutrophication).