Filamentous Bacterial Disease - Bacterial Diseases of Crustaceans

Bacterial Fouling of Surfaces

Filamentous Bacterial Disease

CAUSATIVE AGENT:

Leucothrix sp., Thiothrix sp., Flexibacter sp., Cytophaga sp., Flavobacterium sp.

SPECIES AFFECTED:

Penaeus monodon, P. merguiensis, P. indicus

GROSS SIGNS:

Presence of fine, colorless, thread-like growth on the body surface (Fig. 3-11) and gills as seen under a microscope.

EFFECTS ON HOST:

Infected eggs show a thick mat of filaments on the surface, which may inter-fere with respiration or hatching. In larvae and postlarvae, normal respiration, feeding, locomotion, and molting may be seriously impaired, resulting in slower growth rates, retarded development and eventually death. However, larval shrimps are less prone to infestations due to rapid succession of molts throughout the different larval stages. Frequent molting does not allow ad-equate time for the bacteria to accumulate on the exoskeleton. In larger shrimps, it may result in respiratory distress. Mortality is due to hypoxia. Dis-ease onset is associated with high organic loads in culture water, low dis-solved oxygen levels and added stress from molting. If left untreated in inten-sive culture systems, accumulative mortality may reach 80% or more within a few days to a few weeks of onset of disease signs.

DIAGNOSIS:

Direct microscopic examination of wet mounts of larvae or postlarvae, appendages and gill filaments excised from juvenile or adult shrimp, and of filamentous organisms attached to external surfaces of the cuticle.

PREVENTION AND CONTROL:

•      Maintain good water quality with optimum dissolved oxygen and low organic matter levels.

•      Apply Cutrine Plus at 0.15 ppm copper in 24 h flowthrough treatments

•      Apply 0.5 ppm copper in 4 to 6-h static treatments for PL 2 and older.