Isolation and characterization of a nodavirus associated with mass mortality in Asian seabass (Lates calcarifer) from the west coast of India.

A fish nodavirus was detected in the juveniles of Asian seabass (Lates calcarifer) during a massive outbreak in the seabass cage culture farm located in the south west coast of India. The clinical signs of the disease included anorexia, inflated abdomen, exophthalmia, darkening of the whole body, erratic swimming and cork-screw type movement followed by death. The dead and the moribund fish were analyzed for nodavirus by reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primers targeting the T4 region of RNA2 coat protein gene. This is the first report of nodavirus infection in the fresh water cage-reared seabass fish in the west coast of India. The piscine nodavirus was detected in the brain, retina and kidney of all the fishes examined. The PCR products were cloned and sequenced. The sequence analysis showed more than 90 % homology with the other coat protein gene sequence of piscine nodaviruses from other countries. The phylogenetic analysis based on the partial nucleotide sequence of RNA2 coat protein gene revealed that the virus belonged to the red-spotted grouper nervous necrosis virus, which is one of the widely distributed genotype among the other four known genotypes of piscine nodavirus.