In this study accumulation of some heavy metals Cadmium (Cd), Chromium (Cr), Cobalt (Co), Nickel (Ni) and Lead (Pb) in the operculum, gills, heart, kidney, muscle and vertebrae were determined in some fishes (Hydrocynus forskahlii, Hyperopisus bebe occidentalis and Clarias gariepinus) collected from fishermen around Ogun estuary. The accumulation of the metals in different organs showed significant differences (P<0.05) except lead accumulation. However, the bioaccumulation of the heavy metals was species-related as the accumulations of the heavy metals analysed in the sampled fishes were of the following trend: H. forskahlii > H. bebe occidentalis > C. gariepinus and the pattern of distribution was Ni > Cr > Co > Cd > Pb for all the fish species. The levels of Ni and Cr in this study were higher than the maximum permissible limits (FAO, UNEP, FEPA and WHO) for human consumption and that of Cd, Pb and Co were still lower. Safe disposals of domestic sewage and industrial effluents as well as enforcement of laws enacted to protect our environment are therefore advocated.

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Hematology and histopathological variations in Clarias gariepinus sub-adults subjected to oral challenge with Pseudomonas aeruginosa ATCC27853 were studied for a period of 21 days, with a view to assess the pathogenesis of the bacteria and compared with a control. The results were compared statistically using One-way ANOVA. The symptoms of the infected fish included tail and fin rot, internal hemorrhages and skin patches of superficial ulcers. Tissue sections revealed marked loss and sloughing off of the gill lamellar epithelium, liver showed that hepatocytes appear finely reticulated and foamy; however there were a few foci of large cytoplasmic vacuolations of the hepatocytes and the sinusoids were moderately congested while the intestine showed shortened rugae; the submucosa glands were reduced in numbers; however the surface epithelial cells appeared to be proliferating rapidly and immature (hyperplastic). There was a significant reduction in the mean values of packed cell volume from 34.67±5.2% to 22.33±0.3%, hemoglobin from 9.77±0.2g/dL to 6.97±0.2g/dL, red blood cell from 2.23±0.3x10 12 /L to 1.27±0.1 x10 12 /L and lymphocyte count from 69.00±2.3% to 52.33±0.9% of C. gariepinus after three weeks of exposure to P. aeruginosa. However, the reverse was the case in the mean values obtained for white blood cell and neutrophil for infected fish which were reasonably higher when compared to that of uninfected fish (17.13±0.5 to10.80±0.3x10 9 /L) and (47.33±1.2% to 30.33±2.9%) respectively. It could therefore be concluded that changes in organs and blood parameters of fish occur proportionately to pathogen invasion.

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