Abstract
The severity of pollution within South Africa’s freshwater ecosystems is well known. Of the many pollutants in those ecosystems, heavy metals stand out as a particular source of concern. One of these metals is Cadmium, a known carcinogen with neurodegenerative properties. Neurological effects of Cadmium that have been seen include decreasing the function of Acetylcholine Esterase and causing oxidative damage within neural tissue such as the brain. In fish, it has also been observed that it can decrease olfactory ability over acute exposure periods. Of the neurological studies done on fish exposed to Cadmium, very few focus on the brain’s histology, and very few observe any chronic effects, including studies that focus on effects on olfaction. Also, very few are done on any southern African fish species. In addition, literature has shown that it is very difficult to predict what changes may occur to the neural AChE after exposure to Cadmium, as different species and exposure times show varying results. Furthermore, very few studies look at multiple aspects of effects after exposure. Therefore, this study aimed to determine Cadmium’s multiple effects on the brain, olfactory response, and neural Acetylcholine Esterase activity of South African fish species Oreochromis mossambicus, specifically during acute and chronic exposure periods at an environmentally relevant concentration of 27 μg/L. This study included a behavioural analysis of the olfactory abilities and analysing the histology and activity of AChE within the brain in a control group, an acutely exposed group, and a chronically exposed group. The behavioural analysis revealed decreased olfactory ability in the acute group but not the chronic group. The histology showed no major differences across any structures across any of the groups. The AChE analysis also revealed no significant differences across the groups. The results suggest that O. mossambicus may potentially be able to adapt to protect its brain when exposed to lower concentrations of Cadmium. Further research using higher concentrations that may exceed environmental equivalents, immunohistochemistry to track Cadmium accumulation, and transmission electron microscopy to determine subcellular damage, are recommended.