A comparative health assessment of three fish species from a selected site in the Vaal River, South Africa

M.Sc. (Zoology)The Vaal River system is constantly subjected to pollution from various industrial, mining and agricultural activities. Consequently, pressure is continually exerted on the health of its fish communities and it was suspected that this may be a contributing factor to the repeated fish kills that have occurred in various sections of the river over the past few years. The aim of this study was to assess the health status of three fish species that were affected by the most recent mass fish mortality in the Vaal River. This was done using a combination of techniques including a histology-based health assessment (HHA) that involved a standard fish necropsy, the evaluation of blood parameters as well as a microscopic assessment of the liver, kidney, gills, and gonads. The histological results were semi-quantitatively assessed. Selected chemical substances were also tested for in water, sediment and the skeletal muscle tissue of the fish. Clarias gariepinus, Labeo capensis and Labeo umbratus specimens were collected from the Vaal River, approximately 2480m below the Vaal Dam (Latitude 26°51'17.47"S; Longitude 28° 7'16.58"E) following the latest occurrence of a fish kill in November 2011. Fish were collected using gill nets. Water was sampled in triplicate at three locations, and in situ measurements were done for selected physico-chemical parameters. Sediment samples were also collected and subjected to a sequential extraction technique and quantification of the heavy metals was done using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Metals in skeletal muscle tissue and water were quantified using the same technique. An analysis of variance (ANOVA), followed by the appropriate post-hoc test was performed to determine differences between means of variables i.e. morphometric, histological, substance concentration and blood parameters..