M.Sc. / Aquatic toxicology is the qualitative and quantitative study of toxic effects of pollutants on aquatic organisms. The main goal in toxicity testing is to predict, in combination with other environmental factors, with known accuracy, a concentration of a specific toxicant that will not harm a system and to make this prediction in a responsible and cost effective manner. There are a variety of unique toxicity tests, with fish being one of the most popular organisms to work with, due to being the best-understood organism in the aquatic environment and its commercial importance. Zinc, copper and cadmium are three biologically important heavy metals that are commonly used in various industries. Low concentrations zinc and copper are essential micronutrients for both plants and animals, but in higher concentrations they become toxic to the environment and its biota. Cadmium has a chemical structure similar to that of zinc and is often found in association with it, but it is a very toxic substance. The effects of zinc, copper and cadmium on the free-embryo life stage (yolk sac phase) of Oreochromis mossambicus were examined, for evaluation as a possible ¡§early life stage¡¨ fish lethality assessment. ¡§Fish early life stage tests¡¨ are considered to be relatively quick, comparable and inexpensive screening tools for testing effluents and chemicals. The yolk-sac stage is considered the most sensitive life stage in fish. O. mossambicus free-embryos feed endogenously and are indigenous to southern Africa and are therefore a good choice for lethality testing. The effects of the same metals on randomly selected Culicidae (mosquito) larvae were also tested. The reason for randomly selected larvae was to determine the possibility of doing toxicity testing without a species-specific culture. Mosquitoes are very common and well known due to being vectors of various human diseases. Recommendations towards future studies, to determine the usefulness of both O. mossambicus embryos and Culicidae larvae as biological indicator organisms, were also looked at. / Prof. G.J. Steyn

M.Sc. / Heavy metals occur naturally in the environment and are found in varying levels in all ground and surface waters. Some heavy metals are essential elements for the normal metabolism of organisms, while others are non-essential and play no significant biological role. Anthropogenic activities do, however, cause an increased discharge of these metals into natural aquatic ecosystems. Aquatic organisms are exposed to unnaturally high levels of these metals. Fish are relatively sensitive to changes in their surrounding environment. Fish health may therefore reflect and give a good indication of the health status of a specific aquatic ecosystem. Early toxic effects of pollution may only be evident on cellular or tissue level before significant changes can be identified in fish behaviour or external appearance. Histological analysis appears to be a very sensitive parameter and is crucial in determining cellular changes that may occur in target organs, such as the liver. The liver is a detoxification organ and essential for both the metabolism and excretion of toxic substances in the body. Exposure to heavy metals may cause histological changes in the liver. Fish liver histology could therefore serve as a model for studying the interactions between environmental factors and hepatic structures and functions. In this study, the effect of two heavy metals, cadmium (Cd) and zinc (Zn), on the histology of the liver of the South African freshwater fish species, Oreochromis mossambicus, was investigated. The aim of this study was to determine the toxic effect of cadmium and zinc on the histology of the liver, by identifying significant histological changes in the liver tissue, after exposing the fish to two concentrations of a mixture of cadmium and zinc, over both short and long-term exposure periods. Seventy two, adult O. mossambicus specimens were selected for the study. Two experimental exposures were executed under controlled conditions by means of a flow-through system in an environmental room. For each of the two exposures, twenty-four fish were exposed to different concentrations of cadmium and zinc. The remaining twenty-four specimens were used as a control group. The two respective metal concentrations selected for each exposure were 5% and 10% concentrations of both cadmium and zinc calculated from known LC50 values for cadmium chloride and zinc chloride. Liver samples were fixated in 10% neutrally buffered formalin and prepared for light microscopy analysis using standard techniques for Haematoxylin and Eosin (H & E) and Periodic Acid Schiff (PAS) staining. The liver histology of all seventy two specimens - including the forty eight exposed specimens and twenty four control specimens - were analysed, compared and documented. Although histological analysis can provide a clear indication of the degree of damage caused in the tissue(s) or organ(s) of exposed specimens, the need arises to quantify the histological results in studies where the effects of the exposing substance(s) are compared, to illustrate the possible decrease or increase in histological changes over time or the effect of two different concentrations of the same exposure substance on the histology of the liver. The histological results in this study were quantified in terms of a histological index. An index value representing the specific histological characteristics of the liver was assigned to each individual specimen indicating either normal histological structure (index value of 0-2) or a possible pathological response (index value of 3-6). Histological changes were identified in specimens exposed for 12, 18, 24, and 96 hours to both the 5% and 10% concentrations of cadmium and zinc, indicating a toxic response after the short-term metal exposures. Similar histological changes were identified in both the 5% and 10% exposed livers. These histological changes included hyalnization, vacuolation, cellular swelling and congestion of blood vessels. The liver histology of fish exposed over a long-term period of 672 hours, did, however, appear relatively normal in both the 5% and 10% exposure groups, indicating an adaptative, regenerative response. According to the results obtained, it was clear that exposure period did influence the degree of histological changes identified. The two metal concentrations did however seem to have similar histological effects and no definite variation could be identified in terms of 5% and 10% metal concentrations used. It can therefore be concluded that low concentrations of cadmium and zinc exposure caused histological alterations in the livers of exposed specimens and therefore allows the liver of O. mossambicus to be used as a biomarker of prior exposure to cadmium and zinc. / Dr. G.M. Pieterse

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).