Fish Diseases and Management

5.2.4. Bacterial shell disease

Bacterial shell disease lesions are typically brownish to black in colour. Single or multiple eroded areas on the general body cuticle, appendages, or gills may be present. Lesions may begin as relatively small local lesions (due to abrasions, puncture wounds, chemical trauma or other causes) that rapidly enlarge. This disease is also called as brown spot shell disease / burned spot disease / rust disease / shell disease or black spot disease. Vibrio, Pseudomonas and Beneckea have been known to cause this disease. These organisms cause erosions and ulcerations of the cuticle by their ability to produce lipases, proteases, and chitinases. The black pigment in shell disease lesions is melanin, which is an end product of the crustacean inflammatory response. If not resolved by the shrimps responses, septicaemia and death will be the likely result. The infection can be controlled by provision of better water quality, removal of infected and dead prawns, reducing the stock and adequate nutrition help to control the disease. Reduce the organic load in the pond by increased water exchange. Minimise handling and avoid overcrowding and treatment with formalin 25 ppm in static condition for 24 hrs can be done.