Fish Diseases and Management

5.2.3. Vibriosis in hatcheries

Luminescent bacterial infection in hatcheries cause larval moralities associated with luminescent Vibrio spp. Infected larvae become weak and opaque. Larvae exhibits luminescence when observed in total darkness. Systemic infection results in mortalities in larvae and post larvae reaching up to 100% of the population. The causative bacteria recorded from these penaeid hatcheries were strains of Vibrio parahaemolyticus, V. alginolyticus V. harveyi and V. splendidus. The affected larvae refused to feed. Scanning electron microscopy (SEM) studies indicate that the vibrios colonise specifically the feeding appendages and oral cavity.

Sanitation and rigorous management practices help to control the infestation. The separation of mother shrimps and their faecal matter from the eggs has been done as soon as possible after spawning. Artemia nauplii being used as live feed should be rinsed before introducing into the hatchery during feeding. Initial bacterial load of the rearing water should be minimized by chlorinating and other forms of water treatment like ultraviolet irradiation and filtration. Thorough cleaning, disinfection using 200 ppm chlorinated water and drying of the larval rearing tanks after each cycle of operation helps to control bacterial load and eliminate bacterial pathogens.

Chemical control has limited use because of development of resistant strains of bacteria and limited tolerance of shrimp larvae to the drugs. Hence strict water quality management and sanitation are recommended for preventing luminous vibriosis in penaeid hatcheries.