Scanning Electron Microscopic Studies on the Gills of the Catfish Heteropneustes fossilis (Bloch) Exposed to Copper at Varying pH.

Alterations in gill ultra-structure of the catfish, Heteropneustes fossilis exposed to copper at varying pH were investigated using scanning electron microscopy. Fish were treated with 3 ppm copper sulphate (48 h LC50 concentration at pH 7 ± 0.5) at varying pH of diluent water. Low pH resulted in higher copper (30.01 µg/g dry wt.) accumulation on gills as compared to neutral and high pH treatments, at 18.01 and 16.07 µg/g respectively. Post (48 h) exposure observations included lesions in gills of the treated fish, epithelial lifting, loss of alignment of primary and secondary lamellae, hyperplasia, and hypertrophy of the respiratory epithelium. Fish at pH 5 ± 0.5 showed relatively greater injury compared to pH 8 ± 0.5. The severity of gill damage in copper treated fish followed the sequence of pH 5 ± 0.5 > pH 7 ± 0.5 > pH 8 ± 0.5. Results indicate the synergistic stress caused in fish gill due to acute toxicity of copper and low pH.