What is it?
Grouper iridoviral disease (sleepy grouper disease) is a viral disease that affects the spleen and kidney's of Estuarine rock cod, Malabar grouper and Yellow grouper.
The disease affects fry, juveniles and one to two-year-old market-sized grouper.
Causative agent is a enveloped double-stranded DNA
(dsDNA) virus with a size of 160-200 nm in diameter. Viral replication occurs in the
cytoplasm of the infected cell and virus grows well in cultured fish cell lines derived
from grouper.
Where and when might it occur?
The disease has been officially reported from Hong Kong, Indonesia, the Republic of Korea and Vietnam.
The highest mortalities are usually seen in fish three to four months old after stocking into sea cages.
Horizontal contact and waterborne transmission appear to be the principal ways the virus is spread.
Diagnosis
Fish infected with the disease often become very lethargic and show a decrease in appetite. Fish may also preform rapid opercular movements, dashing to the surface for air. This often occurs in the later stages of the disease. High mortality often follows.
Fish may also show deep ulceration in muscular tissue and red boils on the body surface.
Gross pathological signs are:
- darkened body colour, pale gills and enlarged spleen
- signs of secondary infection such as deep ulceration or papular lesions.
Microscopic pathological signs are:
- necrosis of the splenic pulp and myocardium
- necrosis and reduction of haematopoietic tissue.
Control and treatment
There is currently no control method for the disease.
Source: Australian Government, Department of Agriculture, Fisheries and Forestry