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Chapter: Health Management in Aquaculture: Viral diseases

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Sleepy Grouper Disease (SGD) - Viral Infections In Fish

Affected fish exhibited extreme lethargy and low appetite. Affected fish swim alone or hung at the water surface or remain at the bottom.

Sleepy Grouper Disease (SGD)

CAUSATIVE AGENT:

Iridovirus (130-160 nm)

SPECIES AFFECTED:

Epinephelus tauvina

GROSS SIGNS:

Affected fish exhibited extreme lethargy and low appetite. Affected fish swim alone or hung at the water surface or remain at the bottom.

EFFECT ON HOST:

It was first reported among farmed groupers, 100-200 g and 2-4 kg in size, in 10 of 33 farms in Singapore and Malaysia. Acute disease causes up to 50% mortal-ity mostly occurring during the night or in the early hours of the morning. Gradual mortalities follow after fish become sluggish over 3-5 days, after which affected fish lie at the net or tank bottom exhibiting weak fin movements. Some terminally ill fish display gill pallor, rapid opercular movements and frantic dashing to the water surface to gulp air. Acute mass mortalities may occur 12-24 h after handling or excessive feeding. Internal pathology consists of enlarge-ment of the spleen or occasional enlargement of the anterior kidney and heart inflammation. The virus was detected in the spleen, heart and kidney of in-fected fish. Experimentally exposed fish develop signs of SGD and die in 3-4 days. The virus was introduced into a farm with some imported fish and subse-quently spread to neighboring farms.


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