Affected fish revealed some clinical signs as follows:
Clinical signs related to inflammatory lesions in the CNS, including the brain, spinal cord and retina. Fish lose their appetite and their growth rate is reduced. Fish may be seen whirling and darting in affected fry in the tank in an abnormal manner, as they lose their sight and motor control. They are found either at the top or bottom of the tank as the ability to control their swim bladder is lost. Changes in coloration may also be observed, with species either becoming darker or lighter in color (In affected grouper would be darker and in Barramundi fish it could be lighter).
Here are some pictures about histopathology of Retina and Brain tissues and external signs.
What do you think about mentioned disease and did you have an official report in your country?
Dear Colleagues,
Let me present you more documents about mentioned disorder that have been described.
Hopefully it would be useful for your diagnosis.
According to your discription and histology analysis this is VNN.But you know it without any verification.And there is pity because it is unknown how to treat it.
The clinical signs you describe are typical of Nodavirus infection. Histologically the fish have vacuoles in the brain and the retina. You see abnormal behaviour and spiral movements usually with the belly up, and when you dissect the fish you see over-inflatted swim bladder.
Have checked for noda?
Did you check for the presence of toxic chemical elements in the hypodermal tissue? Even if there is a virus involved, all microbes, and even most organisms, are attracted to particular environments. For instance, mushrooms are do very well in polluted soil. That is why wild harvested mushrooms tend to be very high in metals. The presence of metals can cause the same symptoms you describe.
Some of the symptoms you mentioned such as, whirling and change in colouration, loss of appetite, and clincially inflamtion in CNS simply points to conditions seen in whiriling disease in salmonids. High magnification of histological section may provide even better and more details of the disorder.
Water pollution and as secondary microbial agents such as vnn.
Dear colleagues,
Thank you so much for your valued comments and informative opinion.
Please be consider that affected fish exhibited some erratic swimming patterns and a range of neurological abnormalities, including vacuolization and cellular necrosis in the central nervous system and retina as target tissue.
Which infectious disease can create vacuolization in CNS and retina as Pathognomonic lesion?
The histopathology is consistent with VNN. For the latest Australian information I would recommend downloading Final report- 2008-041-DLD - Aquatic Animal Health Subprogram: Tools for investigation of the nodavirus carrier state in marine, euryhaline and freshwater fish and control of NNV through integrated management. Don't be fooled by the date, its actually Feb 2013, the final report of a study that started in 2008.
at: http://frdc.com.au/research/final-reports/Pages/2008-041-DLD.aspx
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