ASSESSMENT OF HEAVY METALS AND HISTOLOGICAL CONDITIONS OF CHRYSICHTHYS NIGRODIGITATUS (SILVER CATFISH) AND OREOCHROMIS NILOTICUS (TILAPIA) IN OGUN RIVER

ABSTRACT The Ogun River in Nigeria has been subjected to increasing anthropogenic pressures from industrial effluents, agricultural runoff, and domestic waste, resulting in heavy metal pollution and ecological degradation. This study presents a comprehensive ecological risk assessment focusing on two commercially important fish species, Chrysichthys nigrodigitatus (Silver Catfish) and Oreochromis niloticus (Nile Tilapia). The research aimed to link environmental contamination with biological responses, thereby evaluating the implications for aquatic ecosystem health, fisheries sustainability, and food safety. Fish, water, and sediment samples were collected from selected sites along the Ogun River. Morphometric analysis was conducted to assess growth patterns, while histopathological examinations of gill and skin tissues were used to detect structural damage. In addition, concentrations of Manganese (Mn), Zinc (Zn), and Lead (Pb) were quantified in water, sediment, and fish tissues using standard analytical procedures to assess heavy metal bioaccumulation and distribution. The results indicated a negative allometric growth pattern in both fish species, reflecting environmental stress. Histopathological analysis revealed epidermal degeneration and erosion in the skin of both species, while gill lesions were more pronounced in O. niloticus, showing severe necrosis compared to milder erosion in C. nigrodigitatus. Metal analysis revealed elevated Mn and Zn concentrations in water, with O. niloticus exhibiting higher Mn bioaccumulation due to its benthic-associated feeding behavior. Although Pb was present in water and sediment, it was absent in fish tissues, suggesting limited uptake. Overall, the findings demonstrate a clear relationship between anthropogenic pollution and biological impairment in freshwater fish. The Ogun River is significantly compromised by heavy metal contamination, leading to tissue damage, physiological stress, and reduced growth. These outcomes confirm the utility of the studied species as effective bioindicators and emphasize the need for continuous water quality monitoring, strict regulation of pollutant discharge, and integrated biomarker approachesto ensure the sustainable management of Nigerian freshwater resources.