Histopathological changes in two potential indicator fish species from a hyper-eutrophic freshwater ecosystem in South Africa: A baseline study

Histopathological changes were identified in selected target organs from two freshwater fish species, Clarias gariepinus and Oreochromis mossambicus, inhabiting the hyper-eutrophic Roodeplaat Dam near Pretoria. A histology-based fish health assessment protocol was used, including a semiquantitative histopathological assessment of the gills, liver, ovaries, testes, kidney and heart. Water quality analyses showed selected variables to be above the recommended levels, including pH, ammonia, nitrogen, chloride and phosphorus. A number of histopathological alterations were identified in the target organs of both species, with the highest number being in the liver. Species differences were identified in terms of the severity of the alterations within all the organs, with most alterations being regressive in nature. This study provided valuable baseline data that could be useful for future biomonitoring studies.