Incidence of white muscle disease, a viral like disease associated with mortalities in hatchery-reared postlarvae of the giant freshwater prawn Macrobrachium rosenbergii (De Man) from the south-east coast of India

Incidence of post‐larval mortalities of 30–100% was reported from commercial freshwater prawn, Macrobrachium rosenbergii (De Man) hatcheries in Andhra Pradesh and Tamil Nadu (south‐eastern states of India) since 2001. Infected postlarvae (PL) exhibited clinical symptoms with lethargy, anorexia and whitening of abdominal muscles and the disease was identified as white muscle disease (WMD). The waterborne infection of WMD was induced in the laboratory by exposing uninfected and healthy M. rosenbergii PL to the filtered muscle homogenates of the naturally infected PL, resulting in mortality that reached 99% within 10 days post infection. Histopathological examination of the infected animals revealed highly necrotic musculature. Degenerated muscle areas showed aggregations of melanized nuclei, many of which looked like inclusion bodies. Bacteriological examination of affected PL showed the presence of Staphylococcus spp. as a predominant organism, while laboratory challenge of healthy PL with this bacterial isolate did not reproduce WMD.