Reduction of copper-induced histopathological alterations by calcium exposure in Nile tilapia (Oreochromis niloticus)

This study was undertaken to determine whether calcium could render any protection against copper (Cu) toxicity in Nile tilapia with emphasis on histopathological and histochemical analysis. The copper LC(50) values for 24, 48, 72, and 96 h to tilapia in the laboratory were 210.27, 213.34, 193.30, and 185. 75 mg/L, respectively. Prior to Cu exposure, fish were exposed to 0 (G1 and G3) and 30 mg/L calcium carbonate (G2 and G4) for 4 days. After that, fish were exposed to 46 mg/L copper, which corresponds to 25% of the 96 h LC(50) (G3 and G4) for 96 h and 7 days. In the gills of the copper treatment group, primary filament cell hyperplasia, epithelial lifting, or edema, secondary lamellar fusion, and aneurysm were observed. Swollen hepatocytes showing vacuoles and congestion in sinusoids were observed. Necrosis was observed in some areas. In the kidney, glomerulus's atrophy, tubular swelling, and also necrosis were seen. Fish that were pre-exposed to calcium showed slight alteration when compared to copper alone-treatment groups. Histochemical staining for calcium and copper by alizarin red S and rhodanine staining, respectively, indicated no accumulation of calcium and copper in kidney, liver, gills, and muscle. In conclusion, calcium appears to be beneficial in reducing the effects of heavy metal contaminations in aquatic organisms.