Accumulation and histological transformation in the gills, liver, muscles, and skin in Oreochromis niloticus induced by mercury

Specimens of Oreochromis niloticus (One control and 3 experimental groups) were fed diets mixed with different doses of mercury (control group = free of mercury; group 1 = 500 mg/kg; group 2 = 750 mg/kg, and group 3 = 1000 mg/kg) for 60 days in order to study its accumulation and histopathological alterations in the liver, gills, skeletal muscles, and skin. The results obtained revealed that mercury accumulation was significantly (P < 0.05) high in the liver and gills compared to the muscles and skin. The order of accumulation in these organs revealed to be liver > gills > muscles > skin. The fish fed various doses of mercury also showed histological alterations in these organs. Epithelial lifting and epithelial hypertrophy were seen in the gills of the treated fish. Fusion of secondary lamellae was also apparent. The effects were more pronounced in fish fed high doses (1000 mg/kg). Necrosis of hepatocytes and portal veins was also observed in the livers of the treated fish. Irregular muscle bundles and irregularly bigger gaps between the muscle bundles were evident in the skeletal muscles of fish fed diets with mercury, along with some structural changes in the skin of the fish fed mercury-mixed diets. The results obtained clearly indicate that mercury causes deleterious effects on the different organs of fish at even low dose (500 mg/kg).