Abstract
M.Sc.
Two yellowfish species, namely Labeobarbus aeneus and Labeobarbus kimberlyensis were collected in the Vaal Dam and Vaal River Barrage over two years. The macroscopic characteristics, such as dimension and weight were recorded prior to dissecting out the gills. The gills were examined using a stereomicroscope for Paradiplozoon sp., the number of parasites was recorded and they were flat-fixed and stored in 10% Neutral Buffered Formalin. Statistical analysis of host yellowfish dimension and weight, and Paradiplozoon sp. occurrence was performed using Statistical Processing Software Suite v.15.00. The seasonal variation in size and shape of adult life-stage Paradiplozoon sp. attachment clamp sclerites was investigated using the geometric morphometric software Morphologika2 v. 2.5. Water quality variables at the Vaal Dam and Vaal River Barrage were analyzed using RAU Water v.2 software to produce a final Aquatic Toxicity Index Solway aggregate score. Diporpa, juvenile and adult stages of Paradiplozoon sp. were collected from yellowfish in the Vaal Dam, and oncomiracidia were allowed to hatch from eggs that were maintained in vitro. Details of life-stages were examined and measured using light microscopy, epi-fluorescence microscopy, confocal laser scanning microscopy, and scanning electron microscopy.
The Solway aggregate score indicated that the water quality score in the Vaal Dam was better than the Vaal River Barrage. The water quality score was the poorest at both sites in the summer and best during the winter. Turbidity was identified to be the poorest water quality variable. No Paradiplozoon specimens were recovered from the gills of fish from 2005 to 2007 in the Vaal River Barrage. The numbers of Paradiplozoon sp. on yellowfish in the Vaal Dam were the greatest in winter at 67% prevalence, when the water quality score was the best during the study.
In contrast to the elevated diplozoid numbers in rivers of poorer water quality in Europe, a low number of Paradiplozoon sp. were collected in spring when the water quality was poorer. This may be attributed to the difference in the type of aquatic pollutant in the Vaal River and European rivers. Yellowfish were longest and heaviest during spring, followed by autumn, summer and winter. It was not possible to statistically prove whether the presence of Paradiplozoon sp. negatively influences the size and weight of yellowfish.
The increase in weight is suggested to be as a result of increased fat reserves, prior to spawning in spring.