M.Sc. / A comprehensive histology-based fish health assessment was implemented at the Roodeplaat Dam (RD), Pretoria, South Africa, to determine the health status of two fresh water fish species, Clarias gariepinus (n = 20) and Oreochromis mossambicus (n = 18), after exposure to pollutants. RD is known to be polluted, being impacted from two sewage treatment plants, industry, housing and agriculture all upstream of the reserve. Excessive nutrient loads, such as orthophosphate, resulted in the dam becoming eutrophic. The quality of water in the RD was a cause for concern, as the fish from the dam are being used as a source of food by the local people. The histology-based fish health assessment included fish necropsy, calculation of gross body indices and histological assessment. Water quality (chemical and physical) analysis was also carried. Furthermore, target chemical analysis of fish tissue (skeletal muscle) was performed to determine the levels of contaminants in the consumable parts of the fish. These results were compared with existing international guidelines to determine whether the harvested fish were safe for human consumption. All the information obtained was integrated in a qualitative and quantitative scenario-based health risk assessment.

M.Sc. / This study was initiated after a clear need to test and establish a more userfriendly fish species for use in routine laboratory bioassays was identified. This led to a literature review of current toxicity testing species of fish being used, internationally as well as nationally, and identifying which species could possibly be the most suited for use in South African laboratories. From this literature review, it was evident that much emphasis is placed on the practicability of the chosen fish species, and the fact that it can easily be bred within the laboratory, as well as the particular fish specie’s general sensitivity to various toxicants over a wide range of concentrations. The objective of this study is therefore to profile various species of fish to determine which species would be most suited to routine toxicity testing under South African laboratory conditions. This will be done through assimilation of available literature as well as personal communications with people with various expertise and experience in working with the particular fish species. This choice will then be based on the ability of the particular species of fish to ‘balance’ amenability to laboratory conditions with general sensitivity to toxicants. Various indigenous as well as exotic species were therefore selected and tested for suitability for routine testing. Exotic species included Poecilia reticulata and Danio rerio, while the indigenous species tested were Barbus trimaculatus, Barbus argenteus, Tilapia sparrmanii, Oreochromis mossambicus and Pseudocrenilabrus philander philander. Breeding experiments were conducted with all of the abovementioned species and, based on these results; recommendations are made as to which species of fish showed the highest degree of amenability to maintenance within the laboratory.