Effects of selected heavy metals on morphology of Oreochromis niloticus and Clarias gariepinus along Ruiru River, Kenya
Authors: ODONGO KENNETH OUMA , OTIENO SYPRINE A. , SHARMA REKHA R. 
Published: September 2021

Abstract. Ouma KO, Otieno SA, Sharma RR 2019. Effects of selected heavy metals on morphology of Oreochromis niloticus and Clarias gariepinus along Ruiru River, Kenya. Bonorowo Wetlands 9: 86-101. The objective of this study was to determine the levels of heavy metals in tilapia and catfish species along Ruiru River. Sediments, water, and fish samples were collected using systematic random sampling techniques. Three sites were established at downstream of river, 1000 meters of Ruiru Town. The other three were established at upstream of river, 1000 meters of Ruiru Town. Fish samples were transported to the laboratory at National Museums of Kenya for identification. An atomic absorption spectrophotometer was used to examine metals. Fish gills and livers were also examined for histopathological changes. Using one-way analysis of variance, researchers analyzed data on heavy metal levels in water, sediments, and fish gills, livers and muscles. Correlation coefficients were also calculated to assess the relationship between fish length and weight and metal concentrations in fish liver, gills, and muscles, as well as between levels of heavy metals in water and in sediments. In April, 0.167±0.014 mg/L, August, 0.054±0.003 mg/L, and December, 0.222±0.101 mg/L (F = 2.10, p = 0.202), mean chromium levels in water were not statistically significant, but were statistically significant at the downstream sites 0.236±0.019 mg/L, 0.058±0.001 mg/L, and 0.222±0.101 mg/L during the three months (F = 125.63, p<0.001). Significant positive correlations between the levels of iron in sediments and water were found at both upstream and downstream sites, with r = 0.7319, p = 0.025, and r = 0.8506, p = 0.0037, respectively. The linkage between lead levels in sediments and water at upstream sites was not significant (r = 0.343, p = 0.366), while it was significant (r = 0.7523, p = 0.019) at downstream sites. Chromium levels in sediments and water at upstream sites indicated a positive but non-significant connection (r=0.5339, p=0.138). In the downstream sites, there was a substantial positive correlation between chromium levels in sediments and water (r = 0.9787, p<0.001). Metals accumulated in fish tissues in the following order: liver>gills>muscle, and Clarias gariepinus tissues from downstream sites exhibited higher amounts of metals than Oreochromis niloticus tissues from the same sites. In all tissues, both kinds of fish exhibited higher levels of iron than lead, with chromium being the lowest. The liver and gills of fish from the upstream research sites had normal features on histology. Hepatocytes with larger nuclei were found in the livers of fish from downstream sites. The secondary lamellae of the gills had degenerated and fused. Metal levels in sediments were found to be greater than in water, according to the study. Fish from the downstream sites also showed morphological alterations in the liver and gills. The study's findings suggest that people who eat such fish may be exposed to metal poisoning. The National Environment Management Authority should implement measures to reduce industrial trash flow into the Ruiru River, according to the report.