Histopathological disturbances in two fish species Oreochromis niloticus (Linnaeus 1758) and Labeo barbus pellegrini (Bertin et Estève 1948) from downstream mining sites in the upper Ulindi and Elila river basins, Eastern DR Congo

English. peer reviewed

English. The effect of intensive mining on the health status of fish living in the upper basins of the Ulindi and Elila rivers was investigated between June 2018 and March 2022 by comparing the reproductive, hepatic and gill systems of fish collected from sites upstream and downstream of the mining sites. Biometric indices and organ histopathology are biomarkers that were studied at two different trophic levels using two fish species Oreochromis niloticus and Labeobarbus pellegreni. Histological evaluation was performed on the liver, gonads and gills of both species. Water and sediment samples were analysed for total mercury (T-Hg) concentration by (atomic absorption spectrophotometry). Histological changes were assessed semi-quantitatively, and the results were graded according to the severity of the histological responses. The results showed that L. pellegrini accumulated more T-Hg than O. niloticus. The T-Hg level was higher in the organs of both species during the rainy season than during the dry season in the following order: Gonads > Liver > Gills and exceeded the WHO/FAO recommended limit (T-Hg = 1.0 mg/kg wet weight) only in the testes and gills of L. pellegrini collected at the downstream sites of the Ulindi and Elila rivers. This does not necessarily reflect the level in the carcass. Taken together, the results suggest that mercury accumulated downstream of gold mining operations is altering the health of fish populations and that L. pellegrini can be considered a sentinel species for monitoring this pollution. To protect fish health, it is recommended that certain mining practices such as the misuse of mercury be avoided throughout the Congo River basin