Histological Bio Monitoring of the Odimodi River Basin Using the Gills of Sarotherodon melanotheron

Aquatic bodies around industrial points are vulnerable to contamination by pollutants such as petrochemicals, solvents, oils, and heavy metals. Chemical and physical parameters are used as biomarkers to monitor aquatic pollution and to evaluate the adverse effects of heavy metals on aquatic organisms. The use of fish gills as bioindicators is an important biomonitoring tool to evaluate environmental pollution. The histological biomarkers adopted to evaluate the health conditions of different organisms indicate potential environmental hazards. Histotoxicology is applied as an effective method to evaluate the influence of contaminants and other stressors in surface waters. Therefore, histological changes in the gill epithelium of Sarotherodon melanotheron were evaluated and adopted as a bioindicator to measure environmental quality in the Odimodi River basin, Delta State, Nigeria. The study was conducted at the Odimodi river basin in study stations: Station 1, Station 2 and Station 3 for water, soil, sediment and fish sampling, respectively. A purposive sample of 40 fish was collected from the referenced and experimental sites. Light microscopy was used to examine the tissues' histology. The data obtained from this study were analysed using Statistical Packages for Social Sciences (SPSS) version 23 to get the descriptive and inferential statistics, which include mean, frequency tables, and bar charts. Inferential analysis, such as a binomial t-test for independent samples, and P values, was adjusted to minimise type 1 error. It was observed that the referenced site was in good conservation condition, whereas the experimental sites, Locations 1, 2 and 3, showed contamination. The fish species collected from experimental sites showed lesions such as epithelial lifting, vacuolation, and necrosis in the gills. The analysis of the gills obtained from fish collected at the referenced site ARAC showed HAI equal to <10 to <20, indicating reversible and slight organ damage. The total percentage of fish samples collected was 100% for the referenced Site ARAC and the Experimental sites in the Odimodi River Basin. S. melanotheron recorded Regressive Changes: for vacoulation and structural alterations at ARAC 10%, L1 20%, L2 30% and 40%; and Progressive changes: for necrosis and Hyperplasia at ARAC 0%, L1 10%, L2 20 and L3 40%. This study showed histological changes in the fish gills, which suggest the contamination and pollution of the assessed sites caused by heavy metals. Thus, it is necessary to suggest that histological biomarkers be used as the standard bioindicators to measure the environmental status or impact on the environment.