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Chapter: Health Management in Aquaculture: Bacterial diseases

Luminous Bacterial Disease - Internal or Systemic Infections of Crustaceans

Shrimps become weak and opaque-white. Affected shrimps often swim to the pond surface and edges.

Internal or Systemic Infections

Luminous Bacterial Disease

CAUSATIVE AGENT:

Vibrio harveyi (Fig. 3-14) and V. splendidus


SPECIES AFFECTED:

Penaeus monodon, P. merguiensis, and P. indicus

STAGES AFFECTED:

Eggs, larvae, postlarvae, juveniles and adults

GROSS SIGNS:

Shrimps become weak and opaque-white. Affected shrimps often swim to the pond surface and edges. Heavily infected shrimps in tanks and ponds show a continuous greenish glow when observed in total darkness. When viewed un-der the microscope, the hemocoel and internal tissues appear densely packed with active bacteria.

EFFECTS ON HOST:

The hepatopancreas is the target organ of infection. Histopathology shows se-vere inflammation in and around hepatopancreatic tubules of the entire organ. In larger animals, melanized lesions are found in the proximal region of the hepatopancreas. These lesions affect the digestive function of the organ as the necrotic parts become non-functional. Total necrosis and dysfunction lead to death, while partial dysfunction causes slow growth as not all tubules function in digestion, absorption and storage. Systemic infections result in mortality of up to 100%.

DIAGNOSIS:

The disease may be detected by bacteriological (isolation, purification and identification); histological (demonstration of rod-shaped bacteria in tissues of diseased shrimp); and serological [slide agglutination, fluorescent antibody technique (FAT) and enzyme linked immunosorbent assay (ELISA) using spe-cific antibodies] methods.

PREVENTION AND CONTROL:

      Disinfect incoming water and use filtration equipment to prevent entry of luminous bacteria into the hatchery system.

 

     Use only previously disinfected water during spawning and rearing.

 

      Wash eggs.

      Siphon out sediments and debris from the tank bottom.

 

      Disinfect infected stock first before discarding.

 

      Wash and disinfect hatchery paraphernalia after each larval rearing period.

 

      Use microbially mature or aged seawater.

 

      Apply commercially available probiotics to maintain ecological balance within the system.

 

      Use immunoprophylaxis or vaccination.

 

      Monitor bacterial population and diversity in the intake and rearing waters of the shrimp pond.

 

      Apply commercially available probiotics.

 

      Use low salinity rearing water and reservoirs.

 

      Practice crop rotation.

 

      Install greenwater culture system and other system modifications.

 

      The disease may be prevented by rigorous water management.

 

      Apply antibiotics and other antibacterial substances only as the last resort.

 

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