A Quantitative Histological Study On The Influence Of Paper Mill Effluents On The Skin Of Black Spotted Frog

Paper mill effluent is one of the main sources of water pollution that dramatically impacts on biodiversity. Amphibians lack keratin protecting layer on body surface and are easy attacked by toxic substances, therefore, are sensitive to pollutants. However, how amphibians adopt physiological strategies to cope with water pollution has not been well studied except for acute toxicological studies. Reports showed paper mill effluent may change physio-chemical properties of natural water body and directly or indirectly alter the structure of microbial community. Amphibian skin contains granular glands and mucus glands of which the secretions set up a biochemical barrier on the body surface facilitating the natural immunity. It could be hypothesized that amphibians may adjust the structure of skin and glands to response to the changes of water physio-chemical properties and microbial communities due to pollution.This study analyzed the relationship between the changes of water physio-chemical properties and microbial communities and the changes of skin structure of the black spotted frogs (Pelophylax nigromaculata) in a natural water body polluted with paper mill effluent at various extents. Results showed that:1. Lateral folds and warts on skin of the black spotted frog are the major places growing granular glands, making lateral folds the huge reservoir of bioactive molecules that facilitate the animal reacting to severe environmental changes, and making the warts the small and scattering reservoirs secreting bioactive molecules slowly and continuously.2. Species diversity of bacterial community exhibited declining trend with the elevation of pollution extent of paper mill effluent, while the overall abundance of bacteria exhibited an increasing trend.3. With the elevation of pollution extent, the size of granular glands in lateral folds and warts showed a declining trend, while the number of granular glands and relative thickness of epidermis showed an increasing trend. The contribution of bacteria community to these physiological response is greater than of physio-chemical properties of water.4. The black spotted frog has considerable tolerance to paper mill effluent which is mainly resulted from adaptive adjustment of skin physiology.