2. High stocking density with limited water excanhe facilities.  

3. Nutritional deficiency/ poor nourishment.  

4. Accumulation of unutilised feed followed by its purrefaction by the native heterotrophic  
    microorganisms.  

5. Inadequate areation.  

6. Suboptimal or heavy algal blooms in the pond.  

7. Physical injury.  

8. Presence of virulent pathogen in high counts.