Morphological Effects Of Selected Heavy Metals On The Nile Tilapia Oreochromis Niloticus And African Catfish Clarias Gariepinus Along River Ruiru, Kenya

ABSTRACT

River Ruiru flows in areas where it is subject to pollution due to industrial, municipal, urban and agricultural wastes. It is reported to harbor various species of fish such as tilapia, catfish, eel, and common carp, which may be contaminated by heavy metals present in such wastes. Metals damage fish organs, endangering the species inhabiting the river. In addition, when other organisms, including humans consume such fish, they are exposed to heavy metal contamination. Hence, it is important to ascertain that such fish is safe for organisms that consume them. The objective of this study was to determine the levels of heavy metals in tilapia and catfish species along River Ruiru. Systematic random sampling was applied to collect sediments, water and fish samples. Three sites were located downstream along the river, 1000 meters past Ruiru Town. Three control sites were at the upstream sections of the river, 1000 meters away from Ruiru Town. The sampling points were 100 meters apart. Fish samples were transported to the laboratory for identification at the National Museums of Kenya. Metals were analyzed using atomic absorption spectrophotometer. Histopathological changes in gills and liver of fish were also studied. Data on levels of heavy metals in water, sediments and fish gills, liver and muscles were analyzed by means of one way analysis of variance. Correlation coefficients were also calculated to assess the association between length and weight of fish and the concentration of metals in fish liver, gills and muscles, and between levels of heavy metals in water and in sediments. Mean levels of chromium in water were not statistically significant at the upstream sites in April, 0.167±0.014 mg/L, August, 0.054±0.003mg/L, and December, 0.222±0.101mg/L (F = 2.10, p = 0.202), but were statistically significant at the downstream sites 0.236±0.019mg/L, 0.058±0.001mg/L, 0.222±0.101mg/L during the three months respectively (F = 125.63, p < 0.001). Significant positive correlations between the levels of iron in sediments and water at the upstream sites, r = 0.7319, p = 0.025, and in the downstream sites, r = 0.8506, p = 0.0037, were recorded. Correlation in levels of lead in sediments and in water at the upstream sites, r = 0.343, p = 0.366, were not significant, while at the downstream sites, the correlation was significant (r = 0.7523, p = 0.019). Levels of chromium in sediments and water at the upstream sites showed a positive correlation that was not significant (r=0.5339, p=0.138). In the downstream sites, significant positive correlation was noted between levels of chromium in sediments and in water (r = 0.9787, p < 0.001). Metals accumulated in fish tissues in the order liver>gills>muscle, and tissues of Clarias gariepinus from the downstream sites had higher levels of metals compared to tissues of Oreochromis niloticus obtained from the same sites. Both species of fish had higher levels of iron than lead in all the tissues, and level of chromium was the lowest. Histology of liver and gills of fish from the upstream study sites showed normal structures. Liver of fish from downstream sites had enlarged hepatocytes with enlarged nuclei. The gills showed degeneration and fusion of the secondary lamellae. The study showed that sediments had higher levels of metals than water. Morphological changes in liver and gills were also observed in fish obtained from the downstream sites. The findings of the study imply that individuals consuming such fish might be exposed to metal toxicity. The study recommends that the National Environment Management Authority to put in place measures to curb discharge of industrial wastes into River Ruiru. The Kiambu County Department responsible for health should also create awareness to sensitize people not to consume fish from the river.